Heat/acoustic wave conversion component and heat/acoustic wave conversion unit

ABSTRACT

A heat/acoustic wave conversion component having a first end face and a second end face, includes a partition wall that defines a plurality of cells extending from the first end face to the second end face, inside of the cells being filled with working fluid that oscillates to transmit acoustic waves, the heat/acoustic wave conversion component mutually converting heat exchanged between the partition wall and the working fluid and energy of acoustic waves resulting from oscillations of the working fluid. Hydraulic diameter HD of the heat/acoustic wave conversion component is 0.4 mm or less, where the hydraulic diameter HD is defined as HD=4×S/C, where S denotes a cross-sectional area of each cell perpendicular to the cell extending direction and C denotes a perimeter of the cross section, and the heat/acoustic wave conversion component has three-point bending strength of 5 MPa or more.

The present application is an application based on JP 2014-192021 filedon Sep. 19, 2014 with Japan Patent Office, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to heat/acoustic wave conversioncomponents and heat/acoustic wave conversion units. More particularly,the present invention relates to a heat/acoustic wave conversioncomponent to convert heat and acoustic-wave energy mutually, and aheat/acoustic wave conversion unit including a heat/acoustic waveconversion component and a heat exchanger.

Description of the Related Art

Recently society as a whole has been becoming more and more interestedin effective use of energy resources, and so various techniques to reuseenergy have been developed on a trial basis. Among them, an energyrecycling system attracts attention because the acquisition rate (energyefficiency) of the energy acquired is high. The energy recycling systemconverts heat of high-temperature fluid, such as exhaust gas fromautomobiles, to acoustic-wave energy by a thermoacoustic effect, andfinally outputs such energy in the form of electric power. Variousefforts have been made toward the practical use of such a system.

Simply speaking, a thermoacoustic effect is a phenomenon to generateacoustic waves using heat. More specifically, the thermoacoustic effectis a phenomenon to oscillate an acoustic-wave transmitting medium in thethin tube to generate acoustic waves when heat is applied to one endpart of a thin tube to form a temperature gradient at the thin tube.Since it is effective to generate acoustic waves using a large number ofsuch thin tubes at one time, a honeycomb structure including a largenumber of through holes each having a small diameter is often used as acollective form of the thin tubes causing a thermoacoustic effect (seee.g., Patent Documents 1 to 3).

Meanwhile the honeycomb structure itself has been used for variouspurposes, without reference to the thermoacoustic effect, because of itsthree-dimensional geometry having a large surface area. For instance, atypical example is a honeycomb structure to load catalyst for exhaustpurification to remove fine particles from exhaust gas of automobiles,and various types of structures have been developed conventionally.Another example is a honeycomb structure having small through holes of afew tens to a few hundreds μm in diameter, which is developed as an ioncatalyst (see Non-Patent Documents 1, 2, for example). They aremanufactured by a chemical method solely, which is totally differentfrom extrusion that is typically used for honeycomb structures asfilters.

In this way, although honeycomb structures have been well knownconventionally, they are required to have specific properties to besuitable for a thermoacoustic effect when these structures are used asheat/acoustic wave conversion components to exert the thermoacousticeffect. For example, in order to exert a high thermoacoustic effect, thethrough holes preferably have a small diameter, and Patent Document 3proposes a honeycomb structure for a thermoacoustic effect, includingthrough holes having a diameter of 0.5 mm or more and less 1.0 mm thatis smaller than that of honeycomb structures to load catalyst forexhaust purification. Although the honeycomb structures in Non-PatentDocuments 1 and 2 have a very small pore diameter, they are manufacturedby a chemical method solely, and so they have limited lengths anddurability and so are not suitable for the honeycomb structure for athermoacoustic effect very much. On the other hand, the honeycombstructure for a thermoacoustic effect of Patent Document 3 satisfies anecessary condition that is durable in the use as a heat/acoustic waveconversion component to exert a thermoacoustic effect, and then has theadvantage of having an excellent heat/acoustic wave conversion function.

-   [Patent Document 1] JP-A-2005-180294-   [Patent Document 2] JP-A-2012-112621-   [Patent Document 3] JP-A-2012-237295-   [Non-Patent Document 1]    URL:http://www.mesl.t.u-tokyo.ac.jp/ja/research/tpv.html on the    Internet-   [Non-Patent Document 2]    URL:http://www.ricoh.com/ja/technology/tech/009_honeycomb.html on    the Internet

SUMMARY OF THE INVENTION

Patent Document 3, however, does not consider the strength of thecomponent at all that is required for long-term use as a heat/acousticwave conversion component. For instance, when the component is used fora long time as a heat/acoustic wave conversion component, then it willbe always exposed to acoustic wave impacts generated, and so thecomponent has to have a sufficient strength against such acoustic waveimpacts. In this way, honeycomb structures, when they are used as aheat/acoustic wave conversion component, have to be improved more.

In view of the above-mentioned circumstances, the present invention aimsto provide a heat/acoustic wave conversion component having a honeycombstructure and with improved strength, and a heat/acoustic waveconversion unit including such a heat/acoustic wave conversion componentand a heat exchanger.

To fulfill the above-mentioned object, the present invention providesthe following heat/acoustic wave conversion component and heat/acousticwave conversion unit.

[1] A heat/acoustic wave conversion component having a first end faceand a second end face, includes a partition wall that defines aplurality of cells extending from the first end face to the second endface, inside of the cells being filled with working fluid thatoscillates to transmit acoustic waves, the heat/acoustic wave conversioncomponent mutually converting heat exchanged between the partition walland the working fluid and energy of acoustic waves resulting fromoscillations of the working fluid. Hydraulic diameter HD of theheat/acoustic wave conversion component is 0.4 mm or less, where thehydraulic diameter HD is defined as HD=4×S/C, where S denotes an area ofa cross section of each cell perpendicular to the cell extendingdirection and C denotes a perimeter of the cross section, and theheat/acoustic wave conversion component has three-point bending strengthof 5 MPa or more.

[2] In the heat/acoustic wave conversion component according to [1], letthat the heat/acoustic wave conversion component has a length L from thefirst end face to the second end face, a ratio HD/L of the hydraulicdiameter HD to the length L of the heat/acoustic wave conversioncomponent is 0.005 or more and less than 0.02.

[3] In the heat/acoustic wave conversion component according to [1] or[2], the heat/acoustic wave conversion component has an open frontalarea at each end face of 93% or less.

[4] In the heat/acoustic wave conversion component according to any oneof [1] to [3], the cells have a polygonal shape with curved corners as across-sectional shape that is perpendicular to the extending direction,and the corners of the shape have a curvature radius of 0.02 mm or moreand 0.1 mm or less.

[5] In the heat/acoustic wave conversion component according to any oneof [1] to [4], the heat/acoustic wave conversion component includes aporous material having porosity of 5% or less.

[6] In the heat/acoustic wave conversion component according to any oneof [1] to [4], the heat/acoustic wave conversion component includes aporous material having material strength of 20 MPa or more.

[7] In the heat/acoustic wave conversion component according to any oneof [1] to [6], in a plane perpendicular to the extending direction, theheat/acoustic wave conversion component has a first average thickness ofthe partition wall at a center region including a centroid of across-section of the heat/acoustic wave conversion component and havinga shape similar to the cross section, and a second average thickness ofthe partition wall at a circumferential region that is located outsideof the center region and accounts for 20% of an area of thecross-section of the heat/acoustic wave conversion component, the secondaverage thickness being 1.1 to 2.0 times the first average thickness.

[8] In the heat/acoustic wave conversion component according to any oneof [1] to [7], the heat/acoustic wave conversion component includes: aplurality of honeycomb segments, each including a partition wall thatdefines some of the plurality of cells and mutually converting heatexchanged between the partition wall and the working fluid and energy ofacoustic waves resulting from oscillations of the working fluid; abonding part that mutually bonds side faces of the plurality ofhoneycomb segments; and a circumferential wall that surrounds acircumferential face of a honeycomb structure body made up of theplurality of honeycomb segments and the bonding part.

[9] A method for manufacturing the heat/acoustic wave conversioncomponent according to any one of [1] to [8], includes: a forming stepof extruding a forming raw material containing a raw material of theporous material to prepare a honeycomb formed body including a partitionwall that defines a plurality of cells extending from a first end faceto a second end face, a first drying/firing step of drying/firing thehoneycomb formed body prepared by the forming step; a surface layerformation step of bringing a surface of the partition wall in the cellof the honeycomb formed body fired at the first drying/firing step intoa liquid body including at least one type of metal oxide particles ofMg, Si and Al so as to form a surface layer including the at least onetype of metal oxide particles and entering pores on the surface toreduce the pores on the surface; and a second drying/firing step ofdrying/firing the honeycomb formed body having reduced pores on thesurface by the surface layer formation step.

[10] A heat/acoustic wave conversion unit, includes the heat/acousticwave conversion component according to any one of [1] to [8], in a statewhere inside of the plurality of cells is filled with the working fluid,when there is a temperature difference between a first end part on thefirst end face side and a second end part on the second end face side,the heat/acoustic wave conversion component oscillating the workingfluid along the extending direction in accordance with the temperaturedifference and generating acoustic waves; and a pair of heat exchangersthat are disposed in a vicinity of the first end part and the second endpart of the heat/acoustic wave conversion component, respectively, theheat exchangers exchanging heat with the both end parts to give atemperature difference between the both end parts.

[11] A heat/acoustic wave conversion unit includes: the heat/acousticwave conversion component according to any one of [1] to [8], in a statewhere inside of the plurality of cells is filled with the working fluid,and when the working fluid oscillates along the extending directionwhile receiving acoustic waves transmitted, the heat/acoustic waveconversion component generating a temperature difference between a firstend part on the first end face side and a second end part on the secondend face side in accordance with oscillations of the working fluid; aheat exchanger that is disposed in a vicinity of one of the first endpart and the second end part of the heat/acoustic wave conversioncomponent, the heat exchanger supplying heat to the one end part orabsorbing heat from the one end part to keep a temperature at the oneend part constant; and a hot heat/cold heat output unit that is disposedin a vicinity of the other end part of the first end part and the secondend part of the heat/acoustic wave conversion component that is on theopposite side of the one end part, the hot heat/cold heat output unitoutputting hot heat or cold heat obtained from exchanging of heat withthe other end part so that, in a state where the temperature of the oneend part is kept constant by the heat exchanger and when theheat/acoustic wave conversion component receives acoustic wavestransmitted, the other end part has a temperature difference inaccordance with oscillations of the working fluid due to transmission ofthe acoustic waves with reference to the one end part kept at theconstant temperature. Here, “outputting hot heat or cold heat” means,for example, “outputting fluid whose temperature is increased or fluidwhose temperature is decreased”.

Since the heat/acoustic wave conversion component of the presentinvention has hydraulic diameter HD of 0.4 mm or less and three-pointbending strength of 5 MPa or more, the heat/acoustic wave conversioncomponent can have improved strength while keeping sufficient energyconversion efficiency to convert heat into acoustic-wave energy by athermoacoustic effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the configuration of a power generationsystem, to which one embodiment of a heat/acoustic wave conversion unitand a heat/acoustic wave conversion component of the present inventionis applied.

FIG. 2 schematically shows a cold heat generation system, to which theheat/acoustic wave conversion unit and the heat/acoustic wave conversioncomponent in FIG. 1 are applied.

FIG. 3 schematically shows the configuration of the heat/acoustic waveconversion unit of FIG. 1.

FIG. 4 is a perspective view showing the appearance of thehigh-temperature side heat exchanger in the heat/acoustic waveconversion unit of FIG. 3.

FIG. 5 is a cross-sectional view of the high-temperature side heatexchanger when viewing an inflow port and an outflow port of thehigh-temperature side annular tube in a plane.

FIG. 6 schematically shows one form of a heat/acoustic wave conversionunit including another honeycomb structure fitted in thehigh-temperature side annular tube.

FIG. 7 is a schematic cross-sectional view of the high-temperature sideheat exchanger taken along the line A-A of FIG. 6.

FIG. 8 schematically shows another form of the heat/acoustic waveconversion unit of the present invention that is different from theheat/acoustic wave conversion units in FIGS. 6 and 7.

FIG. 9 schematically shows still another form of the heat/acoustic waveconversion unit that is different from the heat/acoustic wave conversionunit in FIG. 8.

FIG. 10 is a cross-sectional view of a high-temperature side heatexchanger having a mesh structure.

FIG. 11 is a cross-sectional view of the heat/acoustic wave conversioncomponent of FIG. 3 in a plane perpendicular to the penetratingdirection of the cells of the heat/acoustic wave conversion component.

FIG. 12 is a cross-sectional view of the heat/acoustic wave conversioncomponent having a segmented structure in a plane perpendicular to thepenetrating direction of the cells.

FIG. 13 shows an example where cells have a triangular shape, andhoneycomb segments have a hexagonal shape.

FIG. 14 is a perspective view showing the appearance of a die that isused to prepare a honeycomb formed body in the present embodiment.

FIG. 15 is a perspective view showing the appearance of the die in FIG.14 that is viewed from the opposite side of FIG. 14.

FIG. 16 is an enlarged plan view showing a part of the surface of thedie in FIG. 14.

FIG. 17 schematically shows a cross section of the die of FIG. 16 takenalong the line A-A′.

FIG. 18 shows an example of the retainer plate configuration.

FIG. 19 shows another example of the retainer plate configuration thatis different from FIG. 18.

FIG. 20 shows still another example of the retainer plate configuration.

FIG. 21 shows a further example of the retainer plate configuration thatis different from FIG. 20.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes embodiments of the present invention, withreference to the drawings. The present invention is not limited to thefollowing embodiments, and is to be understood to include the followingembodiments, to which modifications and improvements are added as neededbased on the ordinary knowledge of a person skilled in the art withoutdeparting from the scope of the present invention.

FIG. 1 schematically shows the configuration of a power generationsystem, to which one embodiment of a heat/acoustic wave conversion unitand a heat/acoustic wave conversion component of the present inventionis applied.

A power generation system 1000 in FIG. 1 includes a heat/acoustic waveconversion unit 100, a looped tube 4, a resonant tube 5 and an energyconverter 6.

The looped tube 4 is a loop-shaped tube that is connected to an end onthe upper side (upper end) and an end on the lower side (lower end) inthe drawing of the heat/acoustic wave conversion unit 100. The resonanttube 5 is a straight tube, having one end connected to the looped tube 4and the other end connected to the energy converter 6. Herein theresonant tube 5 and the energy converter 6 as a whole makes up a tubethat is substantially closed in the end on the right side of thedrawing.

The heat/acoustic wave conversion unit 100 includes a heat/acoustic waveconversion component 1, a high-temperature side heat exchanger 2 and alow-temperature side heat exchanger 3.

The high-temperature side heat exchanger 2 receives the inflow of heatedfluid at high temperatures (e.g., high-temperature exhaust gas), andtransmits the heat thereof to the lower end of the heat/acoustic waveconversion component 1 of FIG. 1 to let the heated fluid having atemperature lower than that at the time of inflow flow out. On the otherhand, the low-temperature side heat exchanger 3 receives the inflow ofcooled fluid (e.g., water) at relatively low temperatures compared withthe heated fluid flowing in the high-temperature side heat exchanger 2and transmits the cold heat to the upper end of the heat/acoustic waveconversion component 1 of FIG. 1 to let the cooled fluid having atemperature higher than that at the inflow flow out. Such functions ofthe high-temperature side heat exchanger 2 and the low-temperature sideheat exchanger 3 yield the state where the lower end of theheat/acoustic wave conversion component 1 has a relatively highertemperature than at the upper end. The heat/acoustic wave conversioncomponent 1 has a honeycomb structure including a plurality of throughholes (hereinafter called cells) like thin tubes that are elongatedvertically in the drawing. Each cell is partitioned from the neighboringcells by a partition wall, and is in communication with the looped tube4 via the high-temperature side heat exchanger 2 and the low-temperatureside heat exchanger 3.

Herein the looped tube 4, the resonant tube 5 and each cell of theheat/acoustic wave conversion component 1 are internally filled withworking fluid that generates oscillations of longitudinal waves andtransmits acoustic waves. An example of the working fluid includes gashaving low viscosity and being less reactive, such as rare gas.

In such a heat/acoustic wave conversion component 1, when there is atemperature difference as stated above at the both ends, the workingfluid in each cell starts to oscillate in the penetrating direction ofthe cells. Then the oscillations are transmitted as acoustic wavesexternally from the heat/acoustic wave conversion component 1. Such aphenomenon of the working fluid oscillating in response to the giventemperature difference is called self-induced oscillations, and is aconventionally well-known phenomenon that occurs when a temperaturegradient is given to a thin tube. A thermoacoustic effect refers togeneration of acoustic waves due to the self-induced oscillation ofworking fluid resulting from heat. The following briefly describes thisself-induced oscillation (a lot of documents describe the details, andPatent Document 3 also provides the detailed descriptions thereon, forexample).

When giving a temperature gradient to a thin tube, then working fluidinside of the thin tube on the high-temperature side absorbs heat fromthe wall surface of the tube and expands from the high-temperature sideto the low-temperature side. Then, the working fluid releases heat tothe wall surface on the low-temperature side and is compressed, and thenreturns back to the high-temperature side. Such exchange of heat withthe wall surface and expansion/compression are repeated, which resultsin oscillation of the working fluid in the elongation direction of thetube. Simply speaking, such motion of the working fluid can said to bethe motion to convey heat so as to alleviate (weaken) the temperaturegradient at the wall surface. As can be clear from this description aswell, such a phenomenon occurs only when the tube is so thin that thethermal effects from the wall surface are large on the working fluidinside. That is, as the tube is made thicker, the thermal effect fromthe wall surface decreases (i.e., it becomes closer to an adiabaticstate), and so such self-induced oscillation hardly occurs. Then, thethickness of the tube is an important factor to generate acoustic wavesby the self-induced oscillation, and the thickness of the tube can beevaluated more quantitatively based on a hydraulic diameter HD that isdefined as HD=4×S/C, where S denotes the cross-sectional area of thetube and C denotes the perimeter of this section.

Referring back to FIG. 1, the power generation system 1000 is describedbelow again.

Since the heat/acoustic wave conversion component 1 includes a pluralityof cells like thin tubes and the self-induced oscillation occurs in eachcell, acoustic waves as the collection of oscillations of the workingfluid in these plurality of cells are then issued from the heat/acousticwave conversion component 1 to the looped tube 4. Then such acousticwaves are transmitted through the looped tube 4 in the direction of thedotted arrows in the drawing. Most of the acoustic waves transmittedthrough the looped tube 4 travels in the resonant tube 5 to the right inthe drawing. As described above, the resonant tube 5 and the energyconverter 6 as a whole makes up a tube that is substantially closed inthe end on the right side of the drawing, and so some of the acousticwaves are reflected and travel to the left in the opposite direction inthe drawing. Then, both of these traveling waves are overlapped in theresonant tube 5. At this time, if the frequency of the traveling wavesmatches with the resonant frequency that is determined, for example, bythe length of the resonant tube 5 then so-called resonance occurs in theresonant tube 5, and steady waves are generated, which are overlappedwaves of both of these traveling waves and have the resonant frequency.In the drawing, the double-headed arrow in the dashed-dotted lineindicates the presence of the steady waves.

Herein the energy converter 6 is equipped with a mechanism not shownthat is capable of changing the effective length of the resonant tube 5,which can adjust the resonance frequency so as to cause the resonance.An exemplary mechanism to change the effective length of the resonanttube 5 includes one described in Patent Document 1, for example.Although the following describes the case where the effective length ofthe resonant tube 5 can be changed, in the power generation system 1000of FIG. 1, a dominant frequency component of the frequency components ofacoustic waves generated at the heat/acoustic wave conversion component1 and traveling through the looped tube 4 may be determined beforehand,and the length of the resonant tube 5 may be configured beforehand to bea special length which makes the frequency of the dominant frequencycomponent the resonance frequency.

The energy converter 6 is equipped with a mechanism to convert acousticwaves into electrical signals as well. An exemplary conversion mechanismof such a type includes a mechanism equipped with a microphone asdescribed in Patent Document 1. Although the conversion mechanismincluding a microphone is the simplest one, the conversion mechanism isnot limited to such a mechanism including a microphone. For instance,conventionally known various mechanisms (e.g., the mechanism of PatentDocument 2), which is to convert acoustic-wave energy to mechanicalenergy and then convert such mechanical energy to electric power byelectromagnetic induction, can be used.

With the configuration as stated above, the power generation system 1000of FIG. 1 can convert heat of high-temperature heated fluid (e.g.,high-temperature exhaust gas) flowing into the high-temperature sideheat exchanger 2 into electric power, and so enables effective use(recycling) of energy.

Next the following describes a cold heat generation system, to which theheat/acoustic wave conversion unit 100 and the heat/acoustic waveconversion component 1 as stated above are applied.

FIG. 2 schematically shows a cold heat generation system, to which theheat/acoustic wave conversion unit 100 and the heat/acoustic waveconversion component 1 in FIG. 1 are applied.

A cold heat generation system 2000 in FIG. 2 includes a looped tube 4′,a transmission tube 5′, an acoustic-wave generation part 7, and theheat/acoustic wave conversion unit 100 described referring to FIG. 1.

The looped tube 4′ is a loop-shaped tube that is connected to an end onthe upper side (upper end) and an end on the lower side (lower end) ofthe heat/acoustic wave conversion unit 100 in FIG. 2, and is incommunication with the plurality of cells of the heat/acoustic waveconversion component 1 via the high-temperature side heat exchanger 2and the low-temperature side heat exchanger 3. The transmission tube 5′is a straight tube, having one end connected to the looped tube 4′ andthe other end connected to the acoustic-wave generation part 7. Theacoustic-wave generation part 7 has a function of generating acousticwaves, and an example of the acoustic-wave generation part 7 includes aspeaker that receives electric power and outputs acoustic waves. Anotherexample is a system that is obtained by removing the energy converter 6from the power generation system 1000 in FIG. 1 and that receives heatand generates acoustic waves (in this case, the resonant tube 5 on theright side is an open end where no reflections occur, and so unlike thestate of FIG. 1, traveling waves toward right are transmitted in theresonant tube 5).

Although the heat/acoustic wave conversion unit 100 has the sameconfiguration as that described with reference to FIG. 1, it isconfigured so that, unlike FIG. 1, cooled fluid (e.g., water), which issimilar to the cooled fluid flowing into the low-temperature side heatexchanger 3 in FIG. 1, flows into both of the high-temperature side heatexchanger 2 and the low-temperature side heat exchanger 3 of FIG. 2.

Herein the looped tube 4′, the transmission tube 5′ and each cell of theheat/acoustic wave conversion component 1 are internally filled withworking fluid that generates oscillations of longitudinal waves andtransmits acoustic waves. Working fluid similar to that used in thepower generation system 1000 of FIG. 1 can be used.

Acoustic waves generated at the acoustic-wave generation part 7 aretransmitted through the transmission tube 5′ in the direction of thedashed-dotted arrow in FIG. 2, and then are transmitted through thelooped tube 4′ in the direction of the dashed line arrow in FIG. 2.Then, the acoustic waves reach the heat/acoustic wave conversion unit100, and travel in each cell from the upper side in FIG. 2 of theheat/acoustic wave conversion component 1. At this time, due to heattransport by acoustic waves, the system can have a state where the endon the high-temperature side heat exchanger 2 side has a relativelyhigher in temperature than the end on the low-temperature side heatexchanger 3 side. At the high-temperature side heat exchanger 2, cooledfluid close to the ambient temperature flows in, and the fluid at atemperature higher than the ambient temperature flows out. On the otherhand, since heat is transported to the end on the high-temperature sideheat exchanger 2 side due to heat transport by acoustic waves, the endof the heat/acoustic wave conversion component 1 on the low-temperatureside heat exchanger 3 side has a temperature lower than the ambienttemperature. Then at the low-temperature side heat exchanger 3, cooledfluid close to the ambient temperature flows in, and the fluid at atemperature lower than the ambient temperature flows out because heat istaken by the end of the heat/acoustic wave conversion component 1 on thelow-temperature side heat exchanger 3 side. In other words, cold heat isoutput in the form of cold water.

With the configuration as stated above, the cold heat generation system2000 in FIG. 2 can output cold heat using acoustic-wave energy generatedat the acoustic-wave generation part 7. Especially when it includes, asthe acoustic-wave generation part 7, the system corresponding to thepower generation system 1000 of FIG. 1 other than the energy converter6, high-temperature heated fluid (e.g., high-temperature exhaust gas)flowing into the high-temperature side heat exchanger 2 of FIG. 1 can beconverted into cold heat, which then enables effective use (recycling)of energy.

As stated above, in the power generation system 1000 in FIG. 1 and thecold heat generation system 2000 in FIG. 2, the heat/acoustic waveconversion unit 100 that is one embodiment of the present inventionplays a very important role. Then the following describes theheat/acoustic wave conversion unit 100 in more details, by way of anexemplary situation where that is used in the power generation system1000 of FIG. 1. The following describes the power generation system 1000of FIG. 1, by way of an example where high-temperature heated fluid(e.g., exhaust gas itself) at about 400 to 600° C. that are typicaltemperatures of the exhaust gas from automobiles flows in thehigh-temperature side heat exchanger 2 of FIG. 1, and low-temperaturecooled fluid (e.g., water) at about 20 to 70° C. flows into thelow-temperature side heat exchanger 3. In this case, a temperaturedifference between both ends of the heat/acoustic wave conversioncomponent 1 is about 330 to 580° C.

Naturally the properties of the heat/acoustic wave conversion unit 100described below are the same as in the case where it is used in the coldheat generation system 2000 of FIG. 2 as well.

FIG. 3 schematically shows the configuration of the heat/acoustic waveconversion unit 100 of FIG. 1.

The heat/acoustic wave conversion unit 100 includes a heat/acoustic waveconversion component 1, a high-temperature side heat exchanger 2 and alow-temperature side heat exchanger 3 as well as a metal member 32 andan interference member 1 a. These components as a whole are stored in ahousing 100 a and are connected to a looped tube 4 (see FIG. 1 also).

The heat/acoustic wave conversion component 1 has a honeycomb structurein which a plurality of cells 14, each being a thin-tube like throughhole, are partitioned and defined by a partition wall 11. Herein, theword “cell” in the present specification refers to a through hole onlythat does not include the partition wall. The heat/acoustic waveconversion component 1 actually may have a structure including severalhoneycomb segments having such a honeycomb structure that are bonded.Such a segmented structure will be described later, and FIG. 3 shows thearrangement of the cells 14 only for ease of explanation. Each cell 14has a penetrating direction (an extending direction in which each cell14 extends) that is the vertical direction of FIG. 3, and is open atboth end faces of an end face on the low-temperature side heat exchanger3 side and an end face of the high-temperature side heat exchanger 2side. The end face of the heat/acoustic wave conversion component 1 onthe low-temperature side heat exchanger 3 side is in contact with themetal member 32, and is opposed to the low-temperature side heatexchanger 3 with the metal member 32 disposed therebetween. Although themetal member 32 is disposed in this case, the present invention may havea form without the metal member 32. When the metal member 32 is omitted,working fluid in contact with a mesh lamination body 30 described lateris cooled, and then the cooled working fluid comes into contact with thevicinity of the end face of the heat/acoustic wave conversion component1 due to the displacement of the working fluid, which corresponds tooscillations of acoustic waves, and cools the vicinity of the end face.When the metal member 32 is omitted, a gap between the heat/acousticwave conversion component 1 and the low-temperature side heat exchanger3 is as small as possible preferably.

The metal member 32 is a metal member having a plate shape, at a centerpart of which a plurality of parallel slits (not shown) are formed, andFIG. 3 shows only a side-face part (thickness part) of the plate shape.

The low-temperature side heat exchanger 3 includes the mesh laminationbody 30 including a plurality of metal mesh plates (e.g., made ofcopper). The low-temperature side heat exchanger 3 includes alow-temperature side annular tube 31 also that is an annular tubesurrounding the side face of the mesh lamination body 30. FIG. 3schematically shows the state where such a low-temperature side annulartube 31 surrounding the side face of the mesh lamination body 30sandwiches the mesh lamination body 30 from both sides at across-section including an inflow port 31 a and an outflow port 31 b.This low-temperature side annular tube 31 has a function of receiving,from the inflow port 31 a, the inflow of cooled fluid (e.g., water) thatis at a relatively low temperature with reference to the heated fluidflowing into the high-temperature side heat exchanger 2 described later,and transmitting cold heat of the cooled fluid to the mesh laminationbody 30 (in other words, transmits heat at the mesh lamination body 30to the cooled fluid) and letting cooled fluid with an increasedtemperature flow out from the outflow port 31 b.

Cold heat transmitted to the mesh lamination body 30 is transmitted tothe working fluid in contact therewith, and is then transmitted to theend face of the heat/acoustic wave conversion component 1 on thelow-temperature side heat exchanger 3 side due to displacement ofacoustic waves to cool the end of the heat/acoustic wave conversioncomponent 1 on the low-temperature side heat exchanger 3 side. To thisend, the metal member 32 is preferably made of a material having largeheat conductivity, which may be made of e.g., copper.

That is the detailed description of the configuration of thelow-temperature side heat exchanger 3, and the heat/acoustic waveconversion unit of the present invention is not limited especially aboutthe details of the low-temperature side heat exchanger, and aconventionally known heat exchanger may be used. The same configurationas that of the high-temperature side heat exchanger 2 described latermay be used.

The side face of the heat/acoustic wave conversion component 1 issurrounded by the interference member 1 a, and FIG. 3 schematicallyshows the cross section of the surrounding interference member 1 a astwo parts that sandwich the heat/acoustic wave conversion component 1from both of right and left sides in the drawing. This interferencemember 1 a has a function as a thermal insulator to avoid heattransmission between the ends of the heat/acoustic wave conversioncomponent 1 on the low-temperature side heat exchanger 3 side and on thehigh-temperature side heat exchanger 2 side via the surroundingenvironment outside of the heat/acoustic wave conversion component 1.

The high-temperature side heat exchanger 2 includes a heat-exchanginghoneycomb structure 20 and a high-temperature side annular tube 21. Theheat-exchanging honeycomb structure 20 has a honeycomb structuresimilarly to the heat/acoustic wave conversion component 1, includingtwo or more cells 20 d, each being a thin-tube like through holepenetrating vertically in FIG. 3, that are partitioned and defined by apartition wall 20 a. The high-temperature side annular tube 21 is anannular tube surrounding the side face of the heat-exchanging honeycombstructure 20, and has a function of receiving, from an inflow port 21 a,the inflow of high-temperature heated fluid (e.g., high-temperatureexhaust gas), transmitting heat of the heated fluid to theheat-exchanging honeycomb structure 20 and letting heated fluid with adecreased temperature flow out from an outflow port 21 b. Then as shownin FIG. 3, the high-temperature side annular tube 21 internally includesa metal or ceramic fin 21 e containing SiC (silicon carbide) as a maincomponent to increase the contact area with the heated fluid.

FIG. 4 is a perspective view showing the appearance of thehigh-temperature side heat exchanger 2 in the heat/acoustic waveconversion unit 100 of FIG. 3, and FIG. 5 is a cross-sectional view ofthe high-temperature side heat exchanger 2, which is a plan viewincluding the inflow port 21 a and the outflow port 21 b of thehigh-temperature side annular tube 21.

As shown in FIG. 4, the high-temperature side heat exchanger 2 includesthe heat-exchanging honeycomb structure 20 that is fitted in a centerhollow part of the annular shape of the high-temperature side annulartube 21. As indicated with thick arrows in FIG. 4, high-temperatureheated fluid (e.g., high-temperature exhaust gas) flows into thehigh-temperature side annular tube 21 from the inflow port 21 a on thelower side of the drawing and flows out from the outflow port 21 b onthe upper side of the drawing. At this time, as indicated with thearrows in FIG. 5, the high-temperature heated fluid flowing in throughthe inflow port 21 a directly hits a circumferential wall 20 b definingthe circular circumference of the heat-exchanging honeycomb structure 20and then is branched off into left and right two sides of thecircumferential wall 20 b and travels along the circumferential wall 20b. Then they join together at the outflow port 21 b to flow out. In thisway, the high-temperature heated fluid directly comes into contact withthe circumferential wall 20 b of the heat-exchanging honeycomb structure20, whereby a lot of heat is directly transmitted from thehigh-temperature heated fluid to the circumferential wall 20 b, and suchheat is transmitted to the partition wall 20 a in the heat-exchanginghoneycomb structure 20 and the working fluid inside of the cells 20 d aswell. In this way, the heat-exchanging honeycomb structure 20 candirectly come into contact with the high-temperature heated fluidbecause the heat-exchanging honeycomb structure 20 is made of a materialhaving high heat resistance and good heat conductivity as describedlater, and such a direct contact with the heated fluid can suppress heatloss and improve heat-exchanging efficiency as compared with the caseincluding another member intervening therebetween.

Although it is preferable that the heat-exchanging honeycomb structure20 directly comes into contact with heated fluid in this way, thepresent invention may have a form in which, instead of such a directcontact of the circumferential wall 20 b of the heat-exchanginghoneycomb structure 20 with high-temperature heated fluid, thecircumferential wall 20 b is surrounded with metal. Especially whenhigh-pressure gas (e.g., inert rare gas such as argon) is used as theworking fluid to transmit acoustic waves, it is preferable to surroundthe circumferential wall 20 b with metal from the viewpoint ofhermetically sealing of such high-pressure gas and avoiding the leakage.In this case, the metal surrounding the circumferential wall 20 b has acircumferential face, on which a metal fin (see fin 21 e in FIG. 3, forexample) is preferably provided so as to protrude in the outwarddirection (radial direction) from the center of the heat-exchanginghoneycomb structure 20 of FIG. 5. This is to increase the contact areawith the high-temperature heated fluid and improve heat-exchangingefficiency. If the contact area with the high-temperature heated fluidis small, exchange of heat between the high-temperature heated fluid andthe high-temperature side heat exchanger 2 is not sufficient, and so theheat-exchanging efficiency of the high-temperature side heat exchanger 2deteriorates. In this way, it is important for the high-temperature sideheat exchanger 2 to maximize the contact area with the high-temperatureheated fluid.

In a most preferable form, another honeycomb structure made of a ceramicmaterial containing SiC (silicon carbide) as a main component is fittedin the tube of the high-temperature side annular tube. This is becausesuch a ceramic material containing SiC (silicon carbide) as a maincomponent has higher heat conductivity at high temperatures than that ofmetal fins, and the contact area with high-temperature gas also can beincreased dramatically. Further, this can avoid a problem of erosion anddeterioration due to high-temperature heated fluid, which can be aproblem for metal fins. The following describes such a preferable form.

FIG. 6 schematically shows one form of a heat/acoustic wave conversionunit including another honeycomb structure fitted in thehigh-temperature side annular tube. FIG. 7 is a schematiccross-sectional view of the high-temperature side heat exchanger takenalong the line A-A of FIG. 6.

In FIGS. 6 and 7, the same reference numerals are assigned to the sameelements as those in FIGS. 3 to 5, and their duplicated descriptions areomitted.

A high-temperature side heat exchanger 2′ in a heat/acoustic waveconversion unit 200 in FIG. 6 includes a heat-exchanging honeycombstructure 20′ and two mutually different high-temperature side annulartubes 211 and 212. The heat-exchanging honeycomb structure 20′ has ahoneycomb structure including two or more cells penetrating horizontallyin the drawing that are partitioned and defined by a partition wall, andtransmits heat transmitted from heated fluid via the two differenthigh-temperature side annular tubes 211 and 212 to the heat/acousticwave conversion component 1. Herein, the heat-exchanging honeycombstructure 20′ is disposed with a distance t from the heat/acoustic waveconversion component 1.

As shown in FIG. 7, the two high-temperature side annular tubes 211 and212 internally include in-tube honeycomb structures 2110 and 2120,respectively, made of a ceramic material containing SiC (siliconcarbide) as a main component. These in-tube honeycomb structures 2110and 2120 both have a honeycomb structure including two or more cellspenetrating horizontally in the drawing that are partitioned and definedby a partition wall. As shown in the arrows of the drawing, heated fluidflowing in the two high-temperature side annular tubes 211 and 212passes through each cell of the in-tube honeycomb structures 2110 and2120, and then flows out. At this time, heat of the heated fluid passingthrough each cell is transmitted to the in-tube honeycomb structures2110 and 2120, and such heat is then transmitted to the heat-exchanginghoneycomb structure 20′ via the wall faces of the high-temperature sideannular tubes 211, 212 and a metal tube (not shown) surrounding the sideface (face of the circumferential wall) of the heat-exchanging honeycombstructure 20′. Although FIG. 7 shows the cross-section of theheat-exchanging honeycomb structure 20′ as a rectangular shape forsimplicity, it may have a circular cross section as in FIGS. 4 and 5,and a substantially similar configuration can be realized when thehigh-temperature side annular tubes 211 and 212 have a shape along thecircle.

In this way, the circumferential wall of the heat-exchanging honeycombstructure 20′ is surrounded with a metal tube, on an outside of whichthe two in-tube honeycomb structures 2110 and 2120 made of a ceramicmaterial containing SiC (silicon carbide) as a main component aredisposed. In this configuration, the heat-exchanging honeycomb structure20′ is not in a direct contact with the heated fluid, and so erosion anddeterioration due to high-temperature heated fluid can be suppressed.When inert rare gas (e.g., argon) is used as the working fluid, aproblem of erosion of the heat-exchanging honeycomb structure 20′ due toworking fluid does not happen. In this case, the heat-exchanginghoneycomb structure 20′ may be made of a metal material having good heatconductivity, such as copper, as well as a ceramic material containingSiC (silicon carbide) as a main component.

Herein, the heat-exchanging honeycomb structure 20′ in FIG. 6 preferablyhas a length L′ of the order of wavelength of acoustic waves generatedfrom oscillations of the working fluid. If the length L′ is too longwith reference to the wavelength of acoustic waves, the heat given tothe working fluid (e.g., inert rare gas) will be insufficient. If thelength L′ is too short with reference to the wavelength of acousticwaves, then working fluid may pass through the heat-exchanging honeycombstructure 20′ from the outside and reach the heat/acoustic waveconversion component 1, and the working fluid at a relatively lowtemperature may cool the end of the heat/acoustic wave conversioncomponent 1 on the high-temperature side heat exchanger sideunfortunately.

FIG. 8 schematically shows another form of the heat/acoustic waveconversion unit of the present invention that is different from theheat/acoustic wave conversion units in FIGS. 6 and 7, and FIG. 9schematically shows still another form of the heat/acoustic waveconversion unit that is different from the heat/acoustic wave conversionunit in FIG. 8.

In the heat/acoustic wave conversion unit of FIG. 8, heated fluid flowsinto the high-temperature side heat exchanger 2A from the upper side ofthe drawing and flows through the high-temperature side heat exchanger2A, and then flows out toward the lower side of the drawing. On theother hand, in the heat/acoustic wave conversion unit of FIG. 9, heatedfluid flows into the high-temperature side heat exchanger 2A′ from theupper side of the drawing and flows through the high-temperature sideheat exchanger 2A′, and then flows out toward the upper side of thedrawing. Herein in both of the heat/acoustic wave conversion units ofFIGS. 8 and 9, cooled fluid flows into the low-temperature side heatexchanger 3A from the upper side of the drawing and flows through thelow-temperature side heat exchanger 3A, and then flows out toward theupper side of the drawing. FIGS. 8 and 9 show the configurationpartially as a perspective view to clarify the internal configurations(configuration including the following two honeycomb structures 22, 23).

The high-temperature side heat exchanger 2A in FIG. 8 and thehigh-temperature side heat exchanger 2A′ in FIG. 9 include apillar-shaped honeycomb structure 23 made of a metal material, and ahollow and round pillar-shaped (in other words, a cylindrical shapehaving a thickness) honeycomb structure 22 made of a ceramic materialcontaining SiC (silicon carbide) as a main component surrounding thehoneycomb structure. At the circumference of the honeycomb structure 23,a metal mesh outer tube 23 a described later, which is made of the samemetal material, is formed integrally with the metal honeycomb structure23. To be precise, a metalized layer, which is described later, ispresent between the two honeycomb structures 22 and 23. These twohoneycomb structures 22 and 23 both have a honeycomb structure includingtwo or more round pillar-shaped cells penetrating in the elongateddirection that are partitioned and defined by a partition wall. Such aconfiguration in FIGS. 8 and 9 also can suppress heat loss and improveheat conversion efficiency.

These embodiments have a honeycomb structure including the honeycombstructure 23 made of a metal material, and instead of this, a meshstructure made up of metal mesh may be used.

FIG. 10 is a cross-sectional view of a high-temperature side heatexchanger having a mesh structure.

The high-temperature side heat exchanger in FIG. 10 includes, inside ofthe honeycomb structure 22 made of a ceramic material containing SiC(silicon carbide) as a main component that is surrounded with a metalouter tube 22 a, a metal mesh member 23′ via a cylindrical metalizedlayer 23 b and a metal mesh outer tube 23 a. Herein the metalized layer23 b is a layer formed by baking of metal such as molybdenum andmanganese, which is a layer to bond the metal mesh outer tube 23 a madeof metal and the honeycomb structure 22 made of ceramic. Theconfiguration in FIG. 10 also can suppress heat loss and improveheat-exchanging efficiency.

Referring back to FIGS. 3 to 5 again, the descriptions are continued inthe following.

As shown in FIG. 3, the end face of the heat-exchanging honeycombstructure 20 on the heat/acoustic wave conversion component 1 side (theupper end face of the heat-exchanging honeycomb structure 20) is in adirect contact with the end face of the heat/acoustic wave conversioncomponent 1 on the high-temperature side heat exchanger 2 side (thelower end face of the heat/acoustic wave conversion component 1).Hereinafter this upper end face of the heat-exchanging honeycombstructure 20 is called a contact face 20 s. Instead of such a directcontact between the heat/acoustic wave conversion component 1 and theheat-exchanging honeycomb structure 20, gap t as in FIG. 6 may bepresent between the heat/acoustic wave conversion component 1 and theheat-exchanging honeycomb structure 20 in the present invention. In thiscase, heat transmitted to the heat-exchanging honeycomb structure 20 istransmitted to working fluid coming into contact with theheat-exchanging honeycomb structure 20, and the heated working fluidcomes into contact with the vicinity of the end face of theheat/acoustic wave conversion component 1 due to displacement of theworking fluid, which corresponds to oscillations of acoustic waves, toheat the vicinity of the end face. This allows the end of theheat/acoustic wave conversion component 1 on the high-temperature sideheat exchanger 2 side to keep a relatively high-temperature state ascompared with the end on the low-temperature side heat exchanger 3 side.

This heat-exchanging honeycomb structure 20 is made of a ceramicmaterial containing SiC (silicon carbide) as a main component. Since aceramic material has high heat resistance, such a material is suitablefor the material of the heat-exchanging honeycomb structure 20 thatdirectly comes into contact with high-temperature heated fluid as statedabove. Further, since a ceramic material containing SiC (siliconcarbide) as a main component has relatively good heat conductivity amongother ceramic materials, such a material is suitable for a function tolet the heat-exchanging honeycomb structure 20 transmit heat to theheat/acoustic wave conversion component 1 as stated above. Note herethat “containing SiC (silicon carbide) as a main component” means thatSiC accounts for 50 mass % or more of the material of theheat-exchanging honeycomb structure 20. At this time, the porosity ispreferably 0 to 10%. It is then preferable that the thickness of thepartition wall 20 a is 0.25 to 0.51 mm and the cell density is 15 to 62cells/cm².

Specific examples of the ceramic material containing SiC as a maincomponent include simple SiC as well as Si impregnated SiC, (Si+Al)impregnated SiC, metal composite SiC, recrystallized SiC, Si₃N₄ and SiC.Among them, Si impregnated SiC and (Si+Al) impregnated SiC arepreferable. This is because Si impregnated SiC has good heatconductivity and heat resistance, and has low porosity although it is aporous body and so is formed densely, and then it can realize relativelyhigh strength as compared with SiC without impregnated Si.

As shown in FIG. 5, the heat-exchanging honeycomb structure 20 has aconfiguration of the triangle cells 20 d that are arranged periodicallywith a period of a constant length in the plane perpendicular to thepenetrating direction of the cells 20 d. As described later, theheat/acoustic wave conversion component 1 to which heat is to betransmitted also has a similar configuration, and the period of thecells 20 d in the heat-exchanging honeycomb structure 20 is integralmultiples of 10 or more of the period of cells 14 in the heat/acousticwave conversion component 1. In this way, the cells 20 d of theheat-exchanging honeycomb structure 20 have the same shape as that ofthe cells 14 of the heat/acoustic wave conversion component 1 to whichheat is to be transmitted, and the period of the cells 20 d of theheat-exchanging honeycomb structure 20 is integral multiples of theperiod of the cells 14 of the heat/acoustic wave conversion component 1,whereby working fluid contained inside the cells 20 d of theheat-exchanging honeycomb structure 20 and the cells 14 of theheat/acoustic wave conversion component 1 can move smoothly. The periodof the cells of the heat-exchanging honeycomb structure 20 is largerthan the period of the cells of the heat/acoustic wave conversioncomponent 1 because the cells 14 of the heat/acoustic wave conversioncomponent 1 are required to be very thin through holes to causeself-induced oscillations as stated above. On the other hand, there isno such a request for the cells 20 d of the heat-exchanging honeycombstructure 20, and the heat-exchanging honeycomb structure 20 may play arole of heat exchange simply, and so the period of them is larger thanthe period of the cells 14 of the heat/acoustic wave conversioncomponent 1 by one digit (ten times) or more.

Note here that when the heat/acoustic wave conversion component 1 has abonded configuration of honeycomb segments described later, thesehoneycomb segments may be arranged periodically with a period of aconstant length, and the period of the cells of the heat-exchanginghoneycomb structure 20 is preferably integral divisions of the period ofthese honeycomb segments (in other words, the period of these honeycombsegments is integral multiples of the period of the cells of theheat-exchanging honeycomb structure 20). This can suppress blocking ofthe cells of the heat-exchanging honeycomb structure 20 at a boundarywith the neighboring honeycomb segments and so can suppress attenuationof acoustic waves. The integral multiples as stated above preferably are5 to 20 times.

As shown in FIG. 3, the contact face 20 s of the heat-exchanginghoneycomb structure 20 with the heat/acoustic wave conversion component1 is displaced toward the heat/acoustic wave conversion component 1(upper side in the drawing) from a heat-receiving region 21 c where theheat-exchanging honeycomb structure 20 directly comes into contact withhigh-temperature heated fluid to receive heat therefrom, and so does notoverlap with the heat-receiving region 21 c. If the contact face 20 soverlaps with the heat-receiving region 21 c, a temperature may differgreatly between the periphery of an edge of the contact face 20 s closerto the heat-receiving region 21 c and a center region away from theheat-receiving region 21 c. In this case, the end (lower end in FIG. 3)of the heat/acoustic wave conversion component 1 on the heat-exchanginghoneycomb structure 20 side is not heated uniformly, and so the cells ofthe heat/acoustic wave conversion component 1 cause non-uniformself-induced oscillations unfortunately. The heat-exchanging honeycombstructure 20 in FIG. 3 is configured so as not to overlap the contactface 20 s with the heat-receiving region 21 c to avoid such a problem.

As shown in FIG. 5, the heat-exchanging honeycomb structure 20 includesa slit 20 c as a gap part of the circumferential wall 20 b, the slitextending in the penetrating direction of the cells 20 d. FIG. 5 showsthe example of slits 20 c formed at four positions of thecircumferential face of the heat-exchanging honeycomb structure 20. Suchslits 20 c can mitigate thermal stress applied to the circumferentialwall 20 b when high-temperature heated fluid directly comes into contactwith the circumferential wall 20 b, which then can suppress breakage orpeeling-off of the circumferential wall 20 b and the partition wall 20a.

As shown in FIG. 5, the high-temperature side annular tube 21 isprovided with four heat-resistant metal plates 21 d along the extendingdirection of the slits 20 c to fill the gaps at the slits 20 c andextend. These four heat-resistance metal plates 21 d can prevent workingfluid from leaking into the high-temperature side annular tube 21through the four slits 20 c. Note here that the heat-exchanginghoneycomb structure 20 is supported by fitting into these fourheat-resistance metal plates 21 d at an annular center part of thehigh-temperature side annular tube 21. These four heat-resistance metalplates 21 d are provided with fins 21 e (see FIG. 3 also) made of metalor ceramic containing SiC (silicon carbide) as a main component, thefins protruding outward (radial direction) from the center of theheat-exchanging honeycomb structure 20 in FIG. 5.

Next, the following describes the heat/acoustic wave conversioncomponent 1 in FIG. 3 in details.

FIG. 11 is a cross-sectional view of the heat/acoustic wave conversioncomponent 1 in FIG. 3 in a plane perpendicular to the penetratingdirection of the cells 14 of the heat/acoustic wave conversion component1.

As shown in FIG. 11, the heat/acoustic wave conversion component 1includes a plurality of cells 14, each being a thin-tube like throughhole, that are partitioned and defined by a partition wall 11, and thepartition wall 11 as a whole is then surrounded with a circumferentialwall 13. The circumferential wall 13 may be made of the same material asthat of the partition wall 11.

As described above, hydraulic diameter HD of the cells 14 is one of theimportant factors to generate acoustic waves by self-inducedoscillations, and so the hydraulic diameter HD of the cells 14 in theheat/acoustic wave conversion component 1 has a very small value of 0.4mm or less. Such cells with a very small hydraulic diameter HD canrealize a sufficient thermoacoustic effect from the heat/acoustic waveconversion component 1. Conversely if the hydraulic diameter HD islarger than 0.4 mm, a very small thermoacoustic effect only can berealized, and then it becomes difficult to obtain sufficient amount ofelectric power and cold heat from the power generation system 1000 inFIG. 1 and the cold heat generation system 2000 in FIG. 2.

The heat/acoustic wave conversion component 1 has a three-point bendingstrength of 5 MPa or more. When the three-point bending strength is 5MPa or more, the heat/acoustic wave conversion component can havesufficient strength against impacts of acoustic waves even when it isalways exposed to acoustic waves by a thermoacoustic effect. If thestrength is too large, the durability of the component may be degradeddue to lack of elasticity, and so 5 MPa or more and 15 MPa or less ispreferable, and 10 MPa or more and 15 MPa or less is particularlypreferable.

The three-point bending strength can be measured by a measuring methodfor the three-point bending strength pursuant to JIS R1601. Morespecifically, a rod-shaped member is cut out from the heat/acoustic waveconversion component 1 to have a size that is specified by JIS R1601 soas to have a length direction in the direction perpendicular to thepenetrating direction of the cells 14. Then, a three-point bending testjig is set while keeping the distances between fulcrums that arespecified by JIS R1601, and the three-point bending (bending) test isconducted in the length direction. The maximum stress before the memberbreaks is measured, and such maximum stress measured is used as thethree-point bending strength.

Herein, the three-point bending strength of the heat/acoustic waveconversion component 1 depends on the material strength of the materialmaking up the heat/acoustic wave conversion component 1, for example.For example, when the material is a porous material, the materialstrength preferably is 20 MPa or more so as to satisfy the numericalrange of the three-point bending strength of the heat/acoustic waveconversion component 1 as stated above. The material strength of thematerial making up the heat/acoustic wave conversion component 1 can beobtained in principle by applying a measurement method similar to thatas stated above to a dense rod-shaped member, which is obtained byfilling the hollow parts in the cell structure of the rod-shaped member,whose three-point bending strength is a target to be measured in thethree-point bending strength measurement of the heat/acoustic waveconversion component 1 as stated above, with the material making up theheat/acoustic wave conversion component 1. Alternatively, such strengthcan be obtained by conversion of the measurement result of thethree-point bending strength of the heat/acoustic wave conversioncomponent 1 while considering the details of the cell structure. Furtheralternatively, a member having the same shape as the rod-shaped memberis formed from a kneaded material that is a raw material of the materialmaking up the heat/acoustic wave conversion component 1, followed bydrying and firing, to prepare a sample as a measurement target of thematerial strength, and the three-point bending strength can be measuredfor this sample by the three-point bending strength measurement asstated above.

When the heat/acoustic wave conversion component 1 is made of a porousmaterial, for example, the three-point bending strength of theheat/acoustic wave conversion component 1 depends on the porosity. Theporosity here is preferably 5% or less so as to satisfy the numericalrange of the three-point bending strength of the heat/acoustic waveconversion component 1 as stated above. The porosity can be measured bya measuring device, such as a mercury porosimeter (e.g., product name:AutoPore IV9505 manufactured by Micromeritics Co.).

When the heat/acoustic wave conversion component 1 is made of a porousmaterial, then it is preferable that a surface layer containing at leastone type of metal oxide particles including Mg, Si and Al is formed onthe surface of the partition wall 11 in each cell (i.e., on inner wallfaces of the cells) so as to reduce the pores on the surface of thepartition wall 11 (on inner wall faces of the cells). Such a surfacelayer can reduce a part of the pores and so reduce the hollow part, andso can improve the strength.

In the heat/acoustic wave conversion component 1, the open frontal areaat the end faces is suppressed to be 93% or less. If the open frontalarea of the cells at the end faces is too high, this means too manyhollows in the heat/acoustic wave conversion component 1 and so degradesthe strength of the heat/acoustic wave conversion component 1.Especially if the open frontal area exceeds 93%, damage on theheat/acoustic wave conversion component 1 due to impacts from generatedacoustic waves cannot be ignored.

In this respect, for a larger thermoacoustic effect, it is advantageousto form as many as possible of the cells having a small hydraulicdiameter as stated above, and so a larger open frontal area at the endfaces of the heat/acoustic wave conversion component 1 is moreadvantageous. Then, the open frontal area of the heat/acoustic waveconversion component 1 is set at a high open frontal area of 60% ormore, although it is 93% or less, from which a large thermoacousticeffect can be achieved. Actually when the open frontal area is less than60%, the number of cells contributing to the thermoacoustic effect istoo small, and so a very large thermoacoustic effect cannot be achievedtherefrom. In this way, the open frontal area at the end faces of theheat/acoustic wave conversion component 1 that is 60% or more and 93% orless can achieve adequate balance between a sufficient thermoacousticeffect and sufficient strength. The open frontal area of 80% or more and93% or less is preferable in the open frontal area of 60% or more and93% or less.

The open frontal area can be obtained by taking an image of a crosssection perpendicular to the penetrating direction by a microscope, anddetermining the material-part area S1 and the gap-part area S2 from thetaken image of the cross section. Then the open frontal area can beobtained as S2/(S1+S2) based on S1 and S2.

Let that L denotes the length between both end faces of theheat/acoustic wave conversion component 1, the heat/acoustic waveconversion component 1 has a ratio HD/L of the hydraulic diameter HD asstated above to the length L that is 0.005 or more and less than 0.02.If HD/L is less than 0.005, the heat/acoustic wave conversion component1 is too long as compared with the hydraulic diameter HD. Then workingfluid in each cell of the heat/acoustic wave conversion component 1 willbe less affected from a temperature difference between both ends of theheat/acoustic wave conversion component. In this case, heat exchangebetween the working fluid in each cell and the partition wall 11 is notsufficient and so a sufficient thermoacoustic effect cannot be obtained.On the other hand, if HD/L is 0.02 or more, then heat/acoustic waveconversion component 1 is too short as compared with the hydraulicdiameter HD. In this case, heat is transmitted through the partitionwall 11 from the high-temperature side heat exchanger 2 side to thelow-temperature side heat exchanger 3 side in the heat/acoustic waveconversion component 1 before heat exchange between the working fluid ineach cell and the partition wall 11 becomes sufficient. As a result, asufficient thermoacoustic effect still cannot be obtained. Then, theheat/acoustic wave conversion component 1 is configured to have theratio HD/L of 0.005 or more and less than 0.02, and so heat exchangebetween the working fluid in each cell and the partition wall 11 issufficient. As a result, the heat/acoustic wave conversion component 1can have a sufficient thermoacoustic effect.

In the heat/acoustic wave conversion component 1, the cells preferablyhave a cross-sectional shape that is perpendicular to the penetratingdirection of the cells 14 such that it is a polygonal shape whosecorners are curved, and the corners of the shape preferably have acurvature radius of 0.02 mm or more and 0.1 mm or less. FIG. 11 shows anexemplary shape of the cells 14 in the enlarged view on the upper rightside, where the triangle has curved corners having the curvature radiusof 0.02 mm or more and 0.1 mm or less. Such a curvature radius of 0.02mm or more means a gently curved shape, and so it can sufficientlyresist an impact acting to crush the cells 14. This is based on the samereason for the shape of a hole such as a tunnel, i.e., a rounded shapeis more resistant to an external force from the surrounding than anangular shape. On the other hand, if the curved part is too large, thenthe partition wall 11 close to the corners of the cells is thick, andaccordingly a part of the through holes as the cells 14 contributing tothe thermoacoustic effect can be reduced. Then, the curvature radius isset at 0.1 mm or less, whereby a high thermoacoustic effect also can bekept at the same time.

The curvature radius at the corners of the cells 14 can be measured bytaking an enlarged photo of the cells 14 in a cross sectionperpendicular to the penetrating direction and based on thecross-sectional shapes of the cells 14.

In a plane perpendicular to the penetrating direction of the cells inthe heat/acoustic wave conversion component 1, an average thickness ofthe partition wall 11 at a circumferential region that is locatedoutside of a center region and accounts for 20% of the area of across-section of the heat/acoustic wave conversion component 1 is 1.1 to2.0 times an average thickness of the partition wall 11 at the centerregion including a centroid of the cross-section of the heat/acousticwave conversion component 1 and having a shape similar to that of thecross section. The partition wall 11 at the circumferential region tendsto receive a force in a specific direction as an external force ascompared with the partition wall 11 at the center region, and externalforces at this region is less mutually canceled although external forcescan be canceled out at the center region. That is why the averagethickness of the partition wall at the circumferential part is thickerthan the average thickness of the partition wall at the center region by1.1 times or more, whereby the strength can be improved. However, if theaverage thickness of the partition wall at the circumferential part istoo thick as compared with the average thickness of the partition wallat the center region, then the cell density at the circumferential partis too small as compared with the cell density at the center region,which leads to a non-uniform thermoacoustic effect between the centerregion and the circumferential part. Then, the average thickness of thepartition wall at the circumferential part may be 2.0 times or less theaverage thickness of the partition wall at the center region, wherebysuch a problem can be avoided.

Thicknesses of the partition wall 11 at the circumferential part and ofthe partition wall 11 at the center region can be obtained by taking anenlarged photo of the cells 14 in a cross section perpendicular to thepenetrating direction and measuring the thickness of the partition wall11.

The material making up the heat/acoustic wave conversion component 1preferably has low heat conductivity of 5 W/mK or less. If the heatconductivity is larger than 5 W/mK, heat is transmitted through thepartition wall 11 from the high-temperature side heat exchanger 2 sideto the low-temperature side heat exchanger 3 side before heat exchangebetween the working fluid in each cell and the partition wall 11 becomessufficient. As a result, a sufficient thermoacoustic effect may not beobtained. On the other hand, such low heat conductivity of 5 W/mK orless leads to sufficient heat exchange between the working fluid in eachcell and the partition wall 11, and so a sufficient thermoacousticeffect can be obtained. Heat conductivity of 1.5 W/mK or less isparticularly preferable in the heat conductive of 5 W/mK or less. If theheat conductivity is too small, then the end face of the heat/acousticwave conversion component 1 on the high-temperature side heat exchanger2 side only has a high temperature locally, meaning a failure totransmit heat to the wall face in the cells and so the difficulty togenerate a thermoacoustic effect. Then, heat conductivity of at least0.01 W/mK is preferable.

The heat conductivity can be obtained by a temperature gradient method(steady method). Specifically, the heat conductivity can be obtained asfollows. Firstly, a plate-shaped test sample is cut out from a targetfor the heat conductivity measurement, and such a plate-shaped testsample is sandwiched between spacers whose heat conductivity is known(e.g., made of metals, such as copper and stainless steel). Then, oneside thereof is heated to 30° C. to 200° C., and the other side iscooled to 20 to 25° C., whereby a certain temperature difference isgiven in the thickness direction of the test sample. Then, the heat flowrate transmitted is obtained by the temperature gradient in the spacers,and this heat flow rate is divided by the temperature difference tocalculate the heat conductivity.

In the heat/acoustic wave conversion component 1, preferably a crosssection of the heat/acoustic wave conversion component 1 in a planeperpendicular to the penetrating direction of the cells 14 has anequivalent circle diameter D of 30 mm or more and 100 mm or less, andthe ratio L/D of the length L of the heat/acoustic wave conversioncomponent 1 to the equivalent circle diameter D is 0.3 or more and 1.0or less.

The “equivalent circle diameter” is defined as D in the representationof the cross-sectional area of the heat/acoustic wave conversioncomponent 1 as πD²/4. The ratio L/D of the length L of the heat/acousticwave conversion component 1 to the equivalent circle diameter D in thenumerical range of 30 mm or more and 100 mm or less may be 0.3 or moreand 1.0 or less, whereby a heat/acoustic wave conversion componenthaving a sufficient thermoacoustic effect and an adequate size can berealized.

Preferably the material making up the heat/acoustic wave conversioncomponent 1 has a ratio of thermal expansion at 20 to 800° C. that is 6ppm/K or less.

Such a ratio of thermal expansion at 20 to 800° C. of 6 ppm/K or less ofthe material making up the heat/acoustic wave conversion component 1 cansuppress damage on the heat/acoustic wave conversion component 1 when atemperature difference occurs at the both ends. A ratio of thermalexpansion of 4 ppm/K or less is more preferable in the ratio of thermalexpansion of 6 ppm/K or less.

Preferably the heat/acoustic wave conversion component 1 has a length Lof 5 mm or more and 60 mm or less.

The heat/acoustic wave conversion component 1 having a length L in theaforementioned numerical range can achieve a sufficient thermoacousticeffect.

Instead of a monolithic honeycomb structure as shown in FIG. 11, theheat/acoustic wave conversion component 1 may include a plurality ofhoneycomb segments each having a configuration similar to that of themonolithic honeycomb structure as in FIG. 11, a bonding part to bondthese plurality of honeycomb segments mutually at their side faces, anda circumferential wall that surrounds the circumferential face of ahoneycomb structure body made up of these plurality of honeycombsegments and their bonding part.

FIG. 12 is a cross-sectional view of the heat/acoustic wave conversioncomponent 1 having a segmented structure in a plane perpendicular to thepenetrating direction of the cells.

The heat/acoustic wave conversion component 1 in FIG. 12 includes aplurality of honeycomb segments 15 each being a monolithicconfiguration, a bonding part 12 to bond the honeycomb segments 15mutually, and a circumferential wall 13 that surrounds the circumferenceof the honeycomb structure body including these bonded members.

A monolithic honeycomb structure as in FIG. 11 may have fluctuations instrength depending on the part in the honeycomb structure manufacturedbecause, in the case of a large-sized honeycomb structure, it issomewhat difficult to manufacture such a structure monolithically. Then,in the case of a large-sized honeycomb structure, it may have abonded-type honeycomb structure including a plurality of separatedhoneycomb segments 15 as in FIG. 12, whereby such fluctuations instrength can be suppressed, and this is an advantage of the bonded typehoneycomb structure.

Herein, the bonded-type honeycomb structure has the lowest strength atthe bonding face (i.e., easy to peel off), and so the three-pointbending strength of the heat/acoustic wave conversion component 1 inFIG. 12 having the bonded-type honeycomb structure is measured as statedabove so that the fracture surface is the bonding face. Then, thethree-point bending strength at this time, i.e., the strength at thebonding face (strength of bonding) may be 5 MPa or more.

In the bonded-type heat/acoustic wave conversion component 1 in FIG. 12,the honeycomb segments 15 have the same properties as various propertiesof the monolithic honeycomb-structured heat/acoustic wave conversioncomponent 1 in FIG. 11 as stated above.

In the heat/acoustic wave conversion component of the present inventionhaving the bonded-type honeycomb structure, each honeycomb segment mayinclude cells 14 having a shape in a plane perpendicular to thepenetrating direction of the cells that are various polygons, such astriangles, quadrangles, pentagons and hexagons as well as ellipses(including a perfect circle shape), where triangles, quadrangles andhexagons and their combinations are preferable. As shown in the enlargedview on the upper right side of the heat/acoustic wave conversioncomponent 1 in FIG. 12 showing the arrangement of the cells 14, it isparticularly preferable to arrange triangle cells 14 periodically insuch a perpendicular plane. For purposes of illustration, thesetriangular cells 14 have corners at acute angles, which, however,actually have curved corners similarly to the cells 14 on the upperright side of FIG. 11.

Such triangular cells 14 are particularly preferable because, amongvarious polygonal shapes and elliptical cell shapes, triangular cellshapes are the most suitable for the arrangement of a lot of cells whileminimizing the thickness of the partition wall. This holds for ahoneycomb structure regardless of whether the honeycomb structure of theheat/acoustic wave conversion component 1 is of a bonded-type or ismonolithic, and for the same reason, triangular cells 14 are used in themonolithic honeycomb structure in FIG. 11 as well. Note here that, inthe case of a honeycomb structure to load catalyst for exhaustpurification to remove fine particles from exhaust gas of automobiles,if their cells have corners at acute angles, fine particles easilyaccumulate at the corners unfortunately. Then, such a honeycombstructure does not actually have triangular cell shapes in many cases,although it can have such a shape in principle. On the other hand, inthe case of a honeycomb structure (honeycomb segment) to exert athermoacoustic effect, such a problem does not happen to working fluid(gas such as rare gas) causing self-induced oscillations, and sotriangular cell shapes, which are the most suitable to arrange a lot ofcells, can be used positively.

When the bonded-type honeycomb structure is used in the presentinvention, a honeycomb segment favorably may have the same shape as thatof the cells so that the shape of the cells is directly reflected,because the honeycomb segment is a collective form of a plurality ofcells, and from the viewpoint of arranging as many as possible of cellson the cross section of the heat/acoustic wave conversion component as awhole. For instance, when the cells 14 have a triangular shape as inFIG. 11, then the honeycomb segments 15 also have a triangular shape sothat the shape of the cells 14 is directly reflected. FIG. 12 shows thestate where triangle honeycomb segments 15 are periodically arranged ina plane of FIG. 12 at a part other than the vicinity of thecircumferential wall 13 of the heat/acoustic wave conversion component1.

Herein, when the cells 14 have a triangular shape, the honeycombsegments may have a hexagonal shape other than a triangular shape. Thisis because a hexagon can be made up of six triangles.

FIG. 13 shows an example where cells have a triangular shape, andhoneycomb segments have a hexagonal shape.

In FIG. 13, the same reference numerals are assigned to the sameelements as those in FIG. 12, and their duplicated descriptions areomitted.

In the heat/acoustic wave conversion component 1′ of FIG. 13, as isunderstood from the arrangement of cells 14 that is indicated on theupper right side of FIG. 13 as an enlarged view, triangular cells 14 areperiodically arranged in a plane perpendicular to the penetratingdirection of the cells 14 in a honeycomb segment 15′. This honeycombsegment 15′ has a hexagonal shape, and a plurality of these hexagonalhoneycomb segments 15′ are periodically arranged in a plane of FIG. 12at a part other than the vicinity of the circumferential wall 13 of theheat/acoustic wave conversion component 1′. Such a form also enables asmany as possible of cells to be arranged on the cross section of theheat/acoustic wave conversion component 1′ as a whole.

Referring back to FIG. 12, the following continues the description ofthe heat/acoustic wave conversion component 1 in FIG. 12. The propertiesof the heat/acoustic wave conversion component 1 described below arecommon to the heat/acoustic wave conversion component 1′ in FIG. 13 aswell.

Preferably in the heat/acoustic wave conversion component 1 in FIG. 12,both of the materials making up the bonding part 12 and thecircumferential wall 13 as stated above have a Young's modulus that isless than 30% of the Young's modulus of the material making up thehoneycomb segments 15, and the material making up the bonding part 12has a thermal expansion coefficient that is 70% or more and less than130% of the thermal expansion coefficient of the material making up thehoneycomb segments 15. Then, the material making up the bonding part 12has heat capacity that is 50% or more of the heat capacity of thematerial making up the honeycomb segments 15.

Such a Young's modulus of the materials making up the bonding part 12and the circumferential wall 13 that is less than 30% of the Young'smodulus of the material making up the honeycomb segments 15 leads to asufficient buffer effect to the thermal stress as stated above. At thistime, if the thermal expansion coefficient and the heat capacity of thebonding part 12 and the circumferential wall 13 differ greatly from thethermal expansion coefficient and the heat capacity of the materialmaking up the honeycomb segments 15 due to a difference in materials,then a problem such as peeling-off occurs between the bonding part 12 orthe circumferential wall 13 and the honeycomb segments 15, and thendurability against thermal stress may be degraded. Then the thermalexpansion coefficient and the heat capacity of the bonding part 12 andthe circumferential wall 13 within the aforementioned numerical rangecan lead to sufficient durability against thermal stress.

The Young's modulus is calculated in the following way. Firstly, aplate-shaped sample having predetermined dimensions is cut out for eachmaterial. The dimensions are those for a plate having a square-shapedface belonging to the range of 10'10 mm to 30×30 mm and a thicknessbelonging to the range of 0.5 to 3 mm, which is common to thesematerials. Let that S denotes the area of the plate-shaped sample (mm²)and t denotes the thickness (mm), then variations Δt (mm) in thethickness of the sample is measured when load W (N) belonging to therange of 0 to 3 MPa is applied to the face of the plate-shaped sample.This load W also is common to these materials. Then, the Young's moduleis calculated by the expression E=(W/S)×(t/Δt), where E denotes theYoung's modulus. Especially in order to find the Young's modulus for thematerial making up the honeycomb segments 15, firstly the Young'smodulus is measured for a sample having a honeycomb structure as statedabove, and then the measured Young's modulus is converted into theYoung's modulus of the material making up the honeycomb segments 15(i.e., the Young's modulus as the material property of the honeycombsegments 15 that is irrespective of the honeycomb structure) consideringthe honeycomb structure.

The thermal expansion coefficient can be obtained pursuant to the“measurement method of thermal expansion of fine ceramics bythermo-mechanical analysis” that is described in JIS R1618-2002. In thismeasurement, a rod-shaped member having the size specified in JISR1618-2002 is cut out from the honeycomb segments 15 so that the lengthdirection of a rod-shaped member to be measured specified in JISR1618-2002 agrees with the penetrating direction of the cells of thehoneycomb segments 15, and then the thermal expansion coefficient isobtained by the method specified in JIS R1618-2002. The thus obtainedthermal expansion coefficient can be used as a thermal expansioncoefficient of the material in the direction agreeing with the cellpenetrating direction.

The heat capacity, e.g., heat capacity per unit volume (e.g., 1 cc) canbe obtained as follows. Firstly, a part of the measurement target ispulverized to be a powder form. Then such a powder-form target is usedas a sample, and then a relationship between input heat and temperaturerise of the sample is examined using an adiabatic calorimeter. In thisway, the heat capacity per unit volume of the sample can be obtained.Then, the thus obtained heat capacity per unit volume is multiplied bydensity (mass per unit volume) of the measurement target used as thesample before pulverization, whereby the heat capacity per unit volume(e.g., 1 cc) can be obtained.

Herein the honeycomb segments 15 preferably include, as a maincomponent, one or two or more in combination of cordierite, mullite,aluminum titanate, alumina, silicon nitride, silicon carbide, and heatresistance resins. Containing “as a main component” means that thematerial accounts for 50 mass % or more of the honeycomb segments 15.Meanwhile, the bonding part 12 and the circumferential wall 13 arepreferably prepared by using a coating material including inorganicparticles and colloidal oxide as a bonding material and an outer coatingmaterial to form the circumferential wall. Exemplary inorganic particlesinclude particles made of a ceramic material containing one or two ormore in combination of cordierite, alumina, aluminum titanate, siliconcarbide, silicon nitride, mullite, zirconia, zirconium phosphate andtitania, or particles of Fe—Cr—Al-based metal, nickel-based metal andsilicon(metal silicon)-silicon carbide based composite materials.Exemplary colloidal oxide includes silica sol and alumina sol. Thesematerials making up the partition wall 11 and the circumferential wall13 are common to the materials making up the partition wall 11 and thecircumferential wall 13 in the monolithic honeycomb structure in FIG. 11as well.

Preferably in the heat/acoustic wave conversion component 1 of FIG. 12,the bonding width of two honeycomb segments 15 mutually bonded is 0.2 mmor more and 4 mm or less, and the ratio of the total cross-sectionalarea of the bonding part 12 to the cross-sectional area of theheat/acoustic wave conversion component 1 in a plane perpendicular tothe penetrating direction of the cells 14 is 10% or less.

Such a bonding width of two honeycomb segments 15 mutually bonded andratio of the total cross-sectional area of the bonding part 12 to thecross-sectional area of the heat/acoustic wave conversion component 1 inthese numerical ranges can lead to sufficient durability against thermalstress while suppressing a decrease in thermoacoustic effect, resultingfrom a decrease in open frontal area due to the bonding part 12.

In the heat/acoustic wave conversion component 1, each of the pluralityof honeycomb segments 15 preferably has a cross-sectional area in aplane perpendicular to the penetrating direction of the cells 14 that is3 cm² or more and 12 cm² or less.

Such a cross-sectional area of each honeycomb segment in theabove-stated numerical range can lead to adequate balance betweensufficient thermoacoustic effect achieved and sufficient durability.

The following describes a method for manufacturing the monolithicheat/acoustic wave conversion component 1 in FIG. 11. The followingdescribes the case where the heat/acoustic wave conversion component 1is made of a ceramic material as an example.

Firstly, binder, surfactant, pore former, water and the like are addedto a ceramic raw material to prepare a forming raw material. The ceramicraw material preferably includes one or two or more in combination of acordierite forming raw material, a silicon carbide-cordierite basedcomposite material, aluminum titanate, silicon carbide, asilicon-silicon carbide based composite material, alumina, mullite,spinel, lithium aluminum silicate, and Fe—Cr—Al based alloy. Among them,a cordierite forming raw material is preferable. Herein the cordieriteforming raw material is a ceramic raw material formulated to have achemical composition in the range of 42 to 56 mass % of silica, 30 to 45mass % of alumina and 12 to 16 mass % of magnesia, and forms cordieriteafter firing. The ceramic raw material preferably is contained to be 40to 90 mass % with reference to the forming raw material as a whole.

Exemplary binder includes methyl cellulose, hydroxypropoxyl cellulose,hydroxyethylcellulose, carboxymethylcellulose, or polyvinyl alcohol.Among them, methyl cellulose and hydroxypropoxyl cellulose arepreferably used together. The content of the binder is preferably 2 to20 mass % with reference to the forming raw material as a whole.

The content of water is preferably 7 to 45 mass % with reference to theforming raw material as a whole.

Exemplary surfactant used includes ethylene glycol, dextrin, fatty acidsoap, or polyalcohol. They may be used alone or in combination of two ormore types. The content of the surfactant is preferably 5 mass % or lesswith reference to the forming raw material as a whole.

The pore former is not limited especially as long as it forms pores byfiring. Exemplary pore former includes starch, foamable resin, waterabsorbable resin or silica gel. The content of the pore former ispreferably 15 mass % or less with reference to the forming raw materialas a whole.

Next, a kneaded material is prepared by kneading the forming rawmaterial. A method for preparing a kneaded material by kneading theforming raw material is not limited especially. For instance, a kneaderor a vacuum pugmill may be used for this purpose.

Next, the kneaded material is extruded, whereby a honeycomb formed bodyis prepared, including a partition wall defining a plurality of cells.For the extrusion, a die having a shape in accordance with the hydraulicdiameter of each cell, the open frontal area, the shape of theheat/acoustic wave conversion component 1, the cell shape, and theperiod of the cells as stated above is preferably used. A preferablematerial of the die is cemented carbide having wear resistance. Valuesof the hydraulic diameter of each cell, the open frontal area, or thelike of the honeycomb formed body are determined, preferably whileconsidering contraction generated during drying and firing describedlater as well.

Herein the heat/acoustic wave conversion component 1 in FIG. 11 having avery small hydraulic diameter of each cell and having a large openfrontal area (having large cell density) as stated above to exert alarger thermoacoustic effect cannot be manufactured by simply using anextrusion method as it is (i.e., by simply executing a similarmanufacturing method using a different die to form high-density pores)that is used for a conventional honeycomb structure to load catalyst forexhaust purification, which is free from such constraints, due to thefollowing two problems.

The first problem is that, during extrusion, kneaded material extrudedat a high temperature adheres to the holes in a forming die, whicheasily generates clogging. This problem is mentioned by Patent Document3 also in paragraph [0021].

The second problem is that a die used for a honeycomb structure as inthe heat/acoustic wave conversion component 1 of FIG. 11 having a verysmall hydraulic diameter of each cell and having a large open frontalarea (having large cell density) inevitably includes a very thin andminute part (typically a part of about 0.3 mm in thickness). Then, sucha minute part often is damaged (e.g., is torn) by viscous frictionduring kneaded material extrusion. Such damage causes deformation of thehoneycomb formed body that cannot be expected, which becomes one of thefactors to degrade the three-point bending strength of the finishedhoneycomb structure.

Then, the manufacturing method of the heat/acoustic wave conversioncomponent 1 has the following configuration to solve these two problems.

For the first problem, prior to the extrusion using a die (hereinaftercalled a real die) corresponding to the heat/acoustic wave conversioncomponent 1 having the hydraulic diameter of each cell that is 0.4 mm orless and the open frontal area that is 60% or more and 93% or less,i.e., having a very small hydraulic diameter of each cell and having alarge open frontal area (having large cell density), a kneaded materialis extruded using another die (hereinafter called a dummy die) having avery small thickness of ribs that is 0.04 mm or more and 0.09 mm orless. The “thickness of ribs” here refers to the thickness of thepartition wall of the honeycomb formed body, and means a slit width ofthe die. Each slit is a hole to discharge the kneaded material and is todetermine the shape of each partition wall part at the honeycombstructure to be manufactured. In the following, the “thickness of ribs”means the slit width. The extrusion using such a dummy die can removebeforehand the component of the kneaded material that tends to be acause of the clogging. Then extrusion by a real die is performed for thekneaded material subjected to the extrusion, whereby clogging as statedabove can be suppressed.

The second problem is solved by reducing viscosity of the kneadedmaterial used for extrusion greatly as compared with the viscosity of akneaded material used for a conventional honeycomb structure to loadcatalyst for exhaust purification so as to reduce the viscous frictionwhile keeping the range of a shape-holding property (i.e. the shape ofthe formed body is not distorted) of the formed body of theheat/acoustic wave conversion component 1 during extrusion. To reducethe viscosity of kneaded material while satisfying the condition to keepa shape-holding property in this way, the ratio of water in the kneadedmaterial has to be more strictly controlled than in the manufacturing ofa conventional honeycomb structure to load catalyst for exhaustpurification (i.e., keeping an error between the control target of thewater ratio and the actual water ratio in a very narrow range).Specifically, the ratio of water in the kneaded material is 40 to 42parts by mass with reference to 100 parts by mass of the kneadedmaterial solid component that is used to manufacture the heat/acousticwave conversion component 1, while the ratio of water in the kneadedmaterial is 25 to 35 parts by mass with reference to 100 parts by massof the kneaded material solid component that is used to manufacture aconventional honeycomb structure to load catalyst for exhaustpurification. When the ratio of water in the kneaded material increases,then viscosity of the kneaded material decreases and adequatefluctuations occur in the shape of the formed body of the heat/acousticwave conversion component 1. This leads to another advantageous effectthat self-induced oscillations of acoustic waves likely occur. Such adecrease in viscosity of the kneaded material has still anotheradvantageous effect of suppressing large deformation that cannot beexpected as stated above, which may affect the strength of the finishedhoneycomb structure (i.e., the heat/acoustic wave conversion component1), and such an effect leads to improved three-point bending strength ofthe finished honeycomb structure.

The following describes a die that is used to prepare a honeycomb formedbody (i.e., extrusion) in the present embodiment. For ease ofexplanation, the following mainly describes the case where cells have aquadrangular shape.

FIG. 14 is a perspective view showing the appearance of a die that isused to prepare a honeycomb formed body in the present embodiment, andFIG. 15 is a perspective view showing the appearance of the die in FIG.14 that is viewed from the opposite side of FIG. 14. FIG. 16 is anenlarged plan view showing a part of the surface of the die in FIG. 14,and FIG. 17 schematically shows a cross section of the die of FIG. 16taken along the line A-A′.

As shown in FIGS. 14 to 17, a die 301 includes a second plate-shapedpart 303, and a first plate-shaped part 307 made of tungsten carbidebased cemented carbide. Herein the second plate-shaped part 303 is madeof at least one type selected from the group consisting of iron, steelmaterials, aluminum alloy, copper alloy, titanium alloy and nickelalloy, and this second plate-shaped part 303 includes a back hole 305 tointroduce the forming raw material of the honeycomb formed body. Thefirst plate-shaped part 307 includes a hole part 311 that is incommunication with the back hole 305, and also includes a slit 309 thatis in communication with the hole part 311 and defines a cell block 313.This first plate-shaped part 307 includes a first layer 307 a disposedon the second plate-shaped part 303 side and a second layer 307 bdisposed on the first layer 307 a. Herein, the hole part 311 is open atboth of the faces of the first layer 307 a, and the slit 309 is open atboth of the faces of the second layer 307 b. FIG. 17 shows the statewhere the hole part 311 has an open end 311 a at a first bonding face310 that agrees with an open end 305 a of the back hole 305 at thesecond bonding face. Such a configuration of the die 301 is to lengthenthe life of the die as described later.

The die 301 preferably has a thickness of 4 to 10 mm. If the thicknessis less than 4 mm, the die may be broken during forming. If thethickness is more than 10 mm, pressure loss is high during forming of ahoneycomb structure, meaning difficulty in forming in some cases.

The second plate-shaped part 303 includes a plate-shaped member made ofat least one type selected from the group consisting of iron, steelmaterials, aluminum alloy, copper alloy, titanium alloy and nickelalloy. Herein steel materials are at least one type selected from thegroup consisting of stainless steel, dies steel and high-speed steel.Among these materials, steel materials are preferable as the material ofthe second plate-shaped part 303, and stainless steel is morepreferable.

In the present application, “at least one type selected from the groupconsisting of iron, steel materials, aluminum alloy, copper alloy,titanium alloy and nickel alloy” may be referred to as “free-machiningmaterial”. The free-machining material is a material that can be easilyground as compared with tungsten carbide based cemented carbide. Sincethe second plate-shaped part 303 does not include the slit 309, wearingis less problematic in the second plate-shaped part 303 than in thefirst plate-shaped part 307. Since the second plate-shaped part 303 ismade of free-machining material, the second plate-shaped part 303 hasexcellent workability as compared with tungsten carbide based cementedcarbide. Further the cost for free-machining material is lower than thatof the tungsten carbide based cemented carbide, and so the manufacturingcost can be reduced.

Stainless steel that is one type of the materials available as thesecond plate-shaped part 303 may be well-known stainless steel. Forinstance, it may be SUS304, SUS303 and the like. The size of the secondplate-shaped part 303 is not limited especially, and it may have adesired size depending on the purpose. Herein when the secondplate-shaped part 303 has a circular plate shape, the diameter of thecircular plate (diameters of one face and the other face) is preferably20 to 40 mm. The thickness of the second plate-shaped part 303 ispreferably 2 to 8 mm. If the thickness is less than 2 mm, it maygenerate deformation and breakage due to stress from forming resistance,and if the thickness is more than 8 mm, forming resistance is excessive,meaning difficulty in extrusion of the formed body.

As described above, the second plate-shaped part 303 includes the backhole 305 to introduce the forming raw material, and the back hole 305 isa through hole (a hole that is open at both faces of the secondplate-shaped part 303) to introduce the forming raw material. When thehoneycomb structure is formed using this die 301, the forming rawmaterial for the honeycomb structure is introduced from the back hole305. The back hole 305 may have any shape as long as it can guide theintroduced forming raw material to the hole part 311 and the slit 309,and the back hole 305 preferably has a circular shape in a cross sectionorthogonal to the flowing direction of the forming raw material(thickness direction of the second plate-shaped part). The open end ofthe back hole 305 preferably has a diameter of 0.15 to 0.45 mm, where0.25 to 0.40 mm is more preferable. Such a back hole 305 can be formedby machine processing, such as electrochemical machining (ECM),electrical discharge machining (EDM), laser processing and drillprocessing, for example. Among these methods, electrochemical machining(ECM) is preferable because ECM can form the back hole 305 effectivelyand precisely. The space in the back hole is preferably in around-pillar shape. In this case, the diameter (diameter of the backhole) in a cross section orthogonal to the flowing direction of theforming raw material (thickness direction of the second plate-shapedpart) in the back hole can have a constant value. In this case, thediameter of the back hole is equal to the diameter of the open end ofthe back hole at the second bonding face. The number of back holes isnot limited especially, which can be decided appropriately depending onthe shape of the honeycomb structure to be manufactured, for example.When the cells have a triangular shape, then the back holes preferablyare disposed at all of the positions corresponding to the intersections(partition wall intersections) where the partition wall mutuallyintersects at the honeycomb structure. When the cells have aquadrangular shape, then the back holes are preferably disposed atalternate intersections of the partition wall of the honeycomb structurein a staggered pattern, whereby adhesiveness of the kneaded material atthe partition wall intersections is favorable, and so the three-pointbending strength of the honeycomb structure is improved. Then, it ispreferable in this case that the back holes are arranged at alternateintersections of the partition wall in a staggered pattern.

The first plate-shaped part 307 includes a plate-shaped member made oftungsten carbide based cemented carbide. The width of the slit 309 isvery narrow as compared with the diameter of the back hole 305. Thismeans that, when the forming raw material is extruded, pressure in theback hole 305 is increased and stress concentrates on the slit 309,which often leads to problems of wearing and deformation, for example.Then, the first plate-shaped part 307 is made of tungsten carbide basedcemented carbide that is a material having wear resistance. Herein,“tungsten carbide based cemented carbide (cemented carbide)” is an alloywhere tungsten carbide and a bonding material are sintered. The bondingmaterial is preferably at least one type of metal selected from thegroup consisting of cobalt (Co), iron (Fe), nickel (Ni), titanium (Ti)and Chromium (Cr). Such tungsten carbide based cemented carbide hasespecially excellent wear resistance and mechanical strength.

The size of the first plate-shaped part 307 is not limited especially,and it may have a desired size in accordance with the purpose. Hereinwhen the first plate-shaped part 307 has a circular plate shape, thediameter of the circular plate is preferably 20 to 40 mm. When the firstplate-shaped part 307 and the second plate-shaped part 303 have acircular plate shape, then the diameter of the first plate-shaped part307 is 90 to 100% of the diameter of the second plate-shaped part 303.The thickness of the first plate-shaped part 307 is preferably 0.3 to1.2 mm, where 0.5 to 0.9 mm is more preferable. The thickness of thefirst plate-shaped part 307 is preferably 0.05 to 2 times the thicknessof the second plate-shaped part 303. Dimensions in such numerical rangescan suppress the deformation of the die itself due to extrusion pressurewithin a tolerable range, and so can avoid large deformation of thepartition wall at the honeycomb structure that may affect thethree-point bending strength of the honeycomb structure.

As described above, the first plate-shaped part 307 includes the firstlayer 307 a disposed on the second plate-shaped part 303 side and thesecond layer 307 b disposed on the first layer 307 a. Since the die 301at the first plate-shaped part includes these two layers of the firstlayer 307 a and the second layer 307 b, stress during extrusion can bemitigated, and so breakage can be prevented. The first layer 307 a andthe second layer 307 b may be made of the same type of materials or ofdifferent types of materials.

In this way, the first layer 307 a is one layer making up the firstplate-shaped part 307, and is disposed on the second plate-shaped part303 side. Herein, the first layer 307 a includes the hole part 311. Thefirst layer 307 a preferably is a layer made of cemented carbide havingVickers hardness of 2,000 to 3,000 HV and having the Young's modulus of600 to 800 GPa. When the first layer 307 a has such Vickers hardness andYoung's modulus, it can be a layer having hardness and toughness thatcan resist the stress applied to the hole part 311. Then problems suchas breakage of the first plate-shaped part 307, which may result fromthe stress from the forming raw material flowing into the hole part 311from the back hole 305, can be prevented, and so the life of the die canbe lengthened. The hole part 311 is open at both faces of the firstlayer 307 a, and so can avoid large deformation of the partition wall atthe honeycomb structure that may affect the three-point bending strengthof the honeycomb structure.

The first layer 307 a preferably has Vickers hardness of 2,000 to 3,000HV, where 2,000 to 2,200 HV is more preferable. With such predeterminedVickers hardness, the first layer 307 a can have hardness so as toresist the stress from the ceramic raw material flowing into the holepart 311 from the back hole 305. Then wearing of the hole part 311 canbe prevented. If the Vickers hardness of the first layer 307 a is lessthan 2,000 HV, wearing may occur due to the lack of strength. If theVickers hardness of the first layer 307 a exceeds 3,000 HV, it is toohard, and so the first layer 307 a may easily break. The first layer 307a preferably has the Young's modulus of 600 to 800 GPa, where 600 to 700GPa is more preferable. This can prevent breakage of the first layer 307a. If the Young's modulus of the first layer 307 a is less than 600 GPa,the toughness is too small, which may cause problems such as breakage.If the Young's modulus exceeds 800 GPa, the toughness is too large,which may lead to the risk of deformation of the hole part 311. When thehoneycomb structure is formed using a die having the deformed hole part311, then distortion occurs at the honeycomb structure and theformability deteriorates.

As described above, the second layer 307 b is one layer making up thefirst plate-shaped part 307, and is disposed on the first layer 307 a.The second layer 307 b includes the slit 309, and the slit 309 is openat both faces of the second layer 307 b. Herein “both faces of thesecond layer 307 b” mean both faces including the face of the secondlayer 307 b in contact with (bonded to) the first layer 307 a and theface on the opposite side (rear side) of the face in contact with thefirst layer 307 a. In FIG. 17, the discharge port of the forming rawmaterial at the slit 309 is indicated as an open end 309 a of the slit309. The second layer 307 b preferably has Vickers hardness of 500 to3,000 HV and the Young's modulus of 400 to 700 GPa. When the secondlayer 307 b has such Vickers hardness and Young's modulus, it can be alayer having sufficient hardness and toughness that can resist thestress applied to the slit 309. Then deformation and wearing of the slit309 can be prevented.

The second layer 307 b preferably has Vickers hardness of 500 to 3,000HV, where Vickers hardness of 2,000 to 3,000 HV is more preferable. SuchVickers hardness can suppress wearing of the second layer 307 b, and socan avoid large deformation of the partition wall at the honeycombstructure that may affect the three-point bending strength of thehoneycomb structure. If the Vickers hardness of the second layer 307 bis less than 500 HV, wearing may occur easily due to the lack ofhardness. If the Vickers hardness exceeds 3,000 HV, the second layer 307b may easily break.

The second layer 307 b preferably has the Young's modulus of 400 to 700GPa, where the Young's modulus of 500 to 700 GPa is more preferable.Such Young's modulus of the second layer 307 b makes the layer hard tobreak. If the Young's modulus of the second layer 307 b is less than 400GPa, problems such as breakage easily occur due to too small toughness.If the Young's modulus exceeds 700 GPa, then the toughness is too large,and so the second layer 307 b easily is deformed.

It is preferable that, in the die 301, the Vickers hardness and theYoung's modulus of the second layer 307 b are larger than the Vickershardness and the Young's modulus of the first layer 307 a. That is, itis preferable that the Vickers hardness of the second layer 307 b islarger than the Vickers hardness of the first layer 307 a, and theYoung's modulus of the second layer 307 b is larger than the Young'smodulus of the first layer 307 a. In such a relationship, the secondlayer 307 b including the slit 309 hardly becomes worn, and the firstlayer 307 a including the hole part 311 hardly breaks. Then, the life ofthe die can be lengthened more due to the second layer 307 b suppressingwearing and the first layer 307 a suppressing breakage, and largedeformation of the partition wall at the honeycomb structure that mayaffect the three-point bending strength of the honeycomb structure canbe avoided.

In the die 301, it is preferable that the Vickers hardness of the secondlayer 307 b is larger than the Vickers hardness of the first layer 307 aby 1,000 to 2,500 HV, and the Young's modulus of the second layer 307 bis larger than the Young's modulus of the first layer 307 a by 50 to 300GPa. Then, the first plate-shaped part 307 can have the second layer 307b having wear resistance and the first layer 307 a having high toughnessreliably, and so the life of the die can be lengthened and largedeformation of the partition wall at the honeycomb structure that mayaffect the three-point bending strength of the honeycomb structure canbe avoided.

The thickness of the first layer 307 a is preferably 0.1 to 5 mm, andthe thickness of the first layer 307 a is 0.2 to 5 mm more preferably.Such a range of the thickness of the first layer 307 a can suppresswearing of the second plate-shaped part effectively. If the thickness ofthe first layer 307 a is less than 0.1 mm, the second plate-shaped parteasily becomes worn. If the thickness of the first layer 307 a exceeds 5mm, pressure during extrusion may increase due to such a thick die. Ifthe pressure during extrusion increases in this way, a difference inpressure between two local points (pressure difference between localpoints) may increase, which may be a factor leading to large deformationof the partition wall at the honeycomb structure that may affect thethree-point bending strength of the honeycomb structure.

The thickness of the second layer 307 b is preferably 0.3 to 4 mm, andthe thickness is 1 to 4 mm more preferably. Such a range of thethickness of the second layer 307 b can suppress deformation of thehoneycomb structure after extrusion, and so the three-point bendingstrength of the honeycomb can be improved. If the thickness of thesecond layer 307 b is less than 0.3 mm, the honeycomb structure afterextrusion may be deformed, which may be a factor leading to largedeformation of the partition wall at the honeycomb structure that mayaffect the three-point bending strength of the honeycomb structure.Wearing and deformation may occur at the second layer 307 b. If thethickness of the second layer 307 b exceeds 4 mm, then the second layer307 b is too thick and so the depth of the slit (the length of the slitin the extruding direction of the forming raw material) is too large, sothat pressure during extrusion becomes too high. In this case, adifference in pressure between local points may increase, which may be afactor leading to large deformation of the partition wall at thehoneycomb structure that may affect the three-point bending strength ofthe honeycomb structure. Further, a part surrounded by the slit isextremely long and thin, and the part may be torn due to friction withkneaded material. In order to prevent such events, a deep slit is notallowed. On the other hand, when the slit is shallow in an adequatedegree, then relative fluctuations in the slit depth increase between aplurality of slits. As a result, the honeycomb structure after extrusionalso can have adequate fluctuations in shape, and so self-inducedoscillations of acoustic waves easily occur.

As stated above, the first plate-shaped part 307 includes the slit 309that is in communication with the hole part 311 and is to form theforming raw material. The slit 309 is a gap (cut) formed in the firstplate-shaped part 307. The forming raw material introduced from the backhole 305 enters the slit 309 in the die, and then the forming rawmaterial is pushed out from the open end 309 a of the slit 309, wherebya formed body in a honeycomb shape can be formed.

As stated above, the slit 309 is open at both faces of the second layer307 b. Although the slit 309 may be formed at the second layer 307 bonly, it is preferable that the slit is formed at the first layer 307 aas well. When it is formed at the first layer 307 a, the slit 309 formedat the second layer 307 b is extended to the first layer side so as tobe formed at the first layer 307 a preferably. In this case, the slit309 at the first layer 307 a is formed at the face of the first layer307 a in contact with the second layer 307 b. Then in this case, thedepth of the slit 309 is larger than the thickness of the second layer307 b. It is preferable that the depth of the slit 309 is 0.3 to 1.0 mm,where 0.4 to 0.8 mm is more preferable. It is preferable that the depthof the slit 309 at a part extended to the first layer side is 0.1 to 0.5mm, where 0.2 to 0.5 mm is more preferable. This can form a formed bodyof a favorable honeycomb shape with less deformation at the partitionwall of the honeycomb structure that may affect the three-point bendingstrength of the honeycomb structure. It is preferable that the width ofthe slit 309 is 0.03 to 0.05 mm, where 0.04 to 0.05 mm is morepreferable.

As described above, the first layer 307 a of the first plate-shaped part307 includes the hole part 311 therein, where this hole part 311 is incommunication with the back hole 305 formed at the second plate-shapedpart 303 and the slit 309 formed at the first plate-shaped part 307. Thehole part 311 is a through hole as well that is formed at the firstlayer 307 a of the first plate-shaped part 307. That is, the hole part311 is a through hole that is open at the face of the second layer 307 bon the side in contact with the second plate-shaped part 303 (the firstbonding face 310 of the first plate-shaped part 307) and is open at theface of the second layer 307 b in contact with the first layer 307 a(the other face 307 ba of the second layer). As shown in FIG. 17, thefirst bonding face 310 is a face of the first plate-shaped part 307 thatis bonded (in contact with) to the second plate-shaped part 303. Such ahole part 311 allows a forming raw material introduced from the backhole 305 formed at the second plate-shaped part 303 to pass through thehole part 311 and enter the slit 309. Then the forming raw material ispushed out from the open end 309 a of the slit 309, whereby a honeycombshaped formed body (honeycomb structure) can be formed. It is preferablethat the depth h of the hole part 311 (see FIG. 17) is 0.1 to 4 mm,where 0.2 to 3 mm is more preferable. Such a range of the depth h of thehole part 311 can suppress wearing at the second plate-shaped part 303effectively, and so can avoid large deformation of the partition wall atthe honeycomb structure that may affect the three-point bending strengthof the honeycomb structure. If the depth h of the hole part is less than0.1 mm, the strength of the first plate-shaped part 307 easilydeteriorates during extrusion of the forming raw material. If the depthh of the hole part exceeds 4 mm, it tends to be difficult to form thehole part by processing the first plate-shaped member during preparationof the die. Herein, the depth h of the hole part 311 is a distance fromthe first bonding face 310 of the first plate-shaped part 307 to theother face 307 ba of the second layer 307 b as shown in FIG. 17. Herein,the depth of the hole part 311 equals the thickness of the first layer307 a. It is preferable that the diameter of the open end 311 a of thehole part 311 is 0.15 to 0.4 mm, where 0.2 to 0.4 mm is more preferable.The hole part 311 may be formed by machine processing, such aselectrochemical machining (ECM), electrical discharge machining (EDM),laser processing and drill processing, for example. Among these methods,electrochemical machining (ECM) is preferable because it can form thehole part 311 effectively and precisely. The space in the hole part 311is preferably in a round-pillar shape. In this case, the diameter(diameter of the hole part 311) in a cross section orthogonal to theflowing direction of the forming raw material (thickness direction ofthe first plate-shaped part) in the hole part 311 can have a constantvalue. At this time, the diameter of the hole part 311 is equal to thediameter of the open end 311 a of the hole part at the first bondingface 310. The number of the hole parts 311 is preferably the same numberas that of the back holes.

As shown in FIG. 17, the die 301 is formed so that the diameter dl ofthe open end 311 a (circle) of the hole part 311 at the first bondingface 310 is the same size as that of the diameter D1 of the open end 305a (circle) of the back hole at the second bonding face 306. As shown inFIG. 17, the second bonding face 306 is a face of the secondplate-shaped part 303 that is bonded to (in contact with) the firstplate-shaped part 307. The open end 311 a of the hole part 311 at thefirst bonding face 310 is an inlet part of the through hole (inflow partof the forming raw material) that is open at the first bonding face 310.The open end 305 a of the back hole 305 at the second bonding face 306is an outlet part (outlet part of the forming raw material) on thesecond bonding face 306 side that is open at the second bonding face 306of the back hole 305. As the forming raw material passes through thisoutlet part, it is then supplied to the hole part 311.

Herein it is preferable that the die includes a retainer plateconfiguration to fix the die for extrusion.

FIG. 18 shows an example of the retainer plate configuration.

In the retainer plate configuration of FIG. 18, the forming raw materialis pushed out in the direction of the downward arrow in FIG. 18. At thistime, a rear retaining part 403 can adjust the amount of kneadedmaterial that flows in. A die 401 is fixed by a retainer 402, and aforming raw material that is pushed out from a gap 405 between the die401 and the retainer 402 defines a circumferential part of a honeycombformed body 404 while being adjusted by an inclined face 406 and anopposed face 407.

FIG. 19 shows another example of the retainer plate configuration thatis different from FIG. 18.

In a retainer plate configuration 550 of FIG. 19, the forming rawmaterial is pushed out in the direction of the downward arrow in FIG.19. This retainer plate configuration 550 includes a back hole 553 tosupply a forming raw material, a die 554 having a slit 552 to push outthe forming raw material and a retaining plate 555 that is disposeddownstream of the die 554. The die 554 includes an inside part 571 and acircumference part 572. The inside part 571 protrudes toward thedownstream (downward in FIG. 19) to define a step height 575 with thecircumference part 572, and this inside part 571 is provided with a slit573 to form a honeycomb structure. The circumference part 572 is thenprovided with a slit 574 that is shorter than the slit 573. Between thedie 554 and the retaining plate 555, a gap part 557 to form the outerwall of the honeycomb structure is formed. Herein a retaining jig 558and a rear-retaining plate 55 a are holders to set the die 554 and theretaining plate 555.

During extrusion using the retainer plate configuration 550 in FIG. 19,the forming raw material is pushed out from the upstream side of the die554 (above in FIG. 19) toward the downstream via the die 554 by anextruder (not shown). The forming raw material 561 that is pushed outfrom the slit 573 at the inside part 571 of the die 554, the slit 573being open on the downstream side, is formed to be a honeycomb structureincluding a lot of cells. On the other hand, the forming raw material561 that is pushed out from the slit 574 at the circumference part 572of the die 554 has a crushed honeycomb shape by the action at the gappart 557, and changes the traveling direction from the pushing-outdirection to the direction toward the step height 575 and changes againthe traveling direction to the pushing-out direction at the place wherethe retaining plate 555 is open so as to form the outer wall surroundingthe cells.

FIG. 20 shows still another example of the retainer plate configuration.FIG. 21 shows a further example of the retainer plate configuration thatis different from FIG. 20.

The retainer plate configuration in FIG. 20(a) includes a die 604 havingslits 602 to form the periodic arrangement of regular triangles as shownin FIG. 20(b). This die 604 is to form a honeycomb structure having aregular triangular cell shape, which is fixed by a retaining plate 605.Herein the slits 602 are in communication with back holes 603. In thisretainer plate configuration, the shape (dimensions) of the honeycombformed body to be formed is determined by the length L1 of the slits602, the length L2 that is obtained by subtracting the height of a stepheight 615 from the length L1 of the slits 602, the width W of the slits602 and the distance d between the retaining plate 605 and the stepheight 615.

FIG. 21 shows a further example of the retainer plate configuration thatis different from FIG. 20.

The retainer plate configuration in FIG. 21(a) includes a die 704 havingslits 702 to form the periodic arrangement of squares as shown in FIG.21(b). This die 704 is to form a honeycomb structure having a squarecell shape, which is fixed by a retaining plate 705. Herein the slits702 are in communication with back holes 703. In this retainer plateconfiguration also, the shape (dimensions) of the honeycomb formed bodyto be formed is determined by the length L1 of the slits 702, the lengthL2 that is a difference between the length L1 of the slits 702 and theheight of a step height 715, the width W of the slits 702 and thedistance d between the retaining plate 705 and the step height 715.

In both of the retainer plate configurations in FIG. 20 and FIG. 21, itis preferable that the length L1 of the slits 702 is 0.3 to 1.0 mm,where 0.4 to 0.8 mm is more preferable. Then it is preferable that thelength L2 as the difference is 0.1 to 0.5 mm to form a favorablehoneycomb formed body with less deformation at the partition wall of thehoneycomb structure that may affect the three-point bending strength ofthe honeycomb structure.

The following continues the description on the following processing forthe honeycomb formed body that is obtained by the extrusion.

The thus obtained honeycomb formed body is dried before firing (firstdrying step). A method for drying is not limited especially, andexemplary methods include an electromagnetic wave heating method such asmicrowave heat-drying and high-frequency induction heating drying and anexternal heating method such as hot air drying and superheated steamdrying. After a certain amount of water may be dried by anelectromagnetic wave heating method, followed by an external heatingmethod to dry the remaining water. In this case, it is preferable that,after 30 to 90 mass % of water with reference to the water amount beforedrying is removed by an electromagnetic heating method, followed by anexternal heating method to reduce water amount to 3 mass % or less. Apreferable electromagnetic wave heating method includes inductionheating drying, and a preferable external heating method includes hotair drying.

If the length of the honeycomb formed body in the cell penetratingdirection is not a desired length, it is preferable to cut both of theend faces (end parts) to have the desired length. Although a method forcutting is not limited especially, exemplary method includes a methodusing a circular saw cutter.

Next, the honeycomb formed body is fired (first firing step). It ispreferable to perform calcination before firing to remove the binder andthe like. The calcination is preferably performed at 400 to 500° C. for0.5 to 20 hours in the ambient atmosphere. A method for calcination orfiring is not limited especially, and they may be performed using anelectric furnace, a gas furnace, or the like. As the firing conditions,it is preferably heated at 1,300 to 1,500° C. for 1 to 20 hours in aninert atmosphere of nitrogen, argon, or the like when a silicon-siliconcarbide based composite material is used, for example. When anoxide-based material is used, it is preferably heated at 1,300 to 1,500°C. for 1 to 20 hours in an oxygen atmosphere.

Next, a liquid body including at least one type of metal oxide particlesof Mg, Si and Al is prepared. Slurry (suspension) or solution is usedfor such a liquid body, and slurry is preferable because it can beeasily prepared. For instance, slurry is prepared, including at leastone type of metal oxide particles of Mg, Si and Al, binder, dispersingagent, surfactant, water and the like. Herein, the binder and thesurfactant may be those as stated above. Such slurry is brought intocontact with the surface of the partition wall in each cell of thehoneycomb formed body after the first firing step (inner wall face ofeach cell), whereby a surface layer is formed there, including at leastone type of metal oxide particles of Mg, Si and Al to enter the pores onthe surface of the partition wall (inner wall face of each cell) andreduce the pores on the surface (surface layer formation step).Exemplary methods to form the surface layer include an immersion methodto immerse the honeycomb formed body after the first firing step inslurry and a flow-down method, in which droplets of slurry are droppeddown from the above into each cell of the honeycomb formed body afterthe first firing step to let the droplets flow down on the inner wallface of the cell. When the flow-down method is used, it is preferablethat flowing-down of droplets of the slurry is repeated a plurality oftimes or after flowing down of droplets of slurry, and that thehoneycomb formed body after the first firing step is turned upside down,followed by flowing-down of droplets of slurry again.

Next, drying processing similar to the first drying step is performed tothe honeycomb formed body after the surface layer formation step (seconddrying step). Then, firing processing similar to the first firing stepis performed to the honeycomb formed body after the second drying step(second firing step).

Finally, if it is required to be a desired cross-sectional shape (e.g.,a circle as in FIG. 11) of the heat/acoustic wave conversion component1, the circumferential part of the honeycomb formed body after thesecond firing step is cut as needed to correct the shape. Then, an outercoating material is applied to the circumferential face of the honeycombformed body after cutting, followed by drying, whereby a circumferentialwall 13 is formed. Herein, the outer coating material used may be thesame material as that of the bonding material described later. A methodfor applying the outer coating material is not limited especially, andfor example, the coating material may be coated with a rubber spatula,for example, while rotating the honeycomb formed body after cutting on awheel.

Through these steps, the monolithic heat/acoustic wave conversioncomponent 1 in FIG. 11 is finally completed.

When the bonded-type heat/acoustic wave conversion component 1 in FIG.12 is manufactured, a plurality of honeycomb segments 15 in FIG. 12 isprepared through almost the same steps as those for the monolithicheat/acoustic wave conversion component 1 in FIG. 11 as stated aboveother than the final step to apply the outer coating material. Herein,since the honeycomb segments 15 in FIG. 12 have a triangularcross-sectional shape, it is required to involve some modification suchthat a die suitable for such a triangular cross-sectional shape is usedin the manufacturing method of the heat/acoustic wave conversioncomponent 1 in FIG. 11 as stated above, or the shape is corrected to bea triangle by cutting.

Then these prepared plurality of honeycomb segments 15 are arranged sothat their side faces are opposed, which are then bonded with a bondingmaterial that is a material before solidification of the bonding part12, followed by drying. A method to apply the bonding material to theside faces of the honeycomb segments is not limited especially, and aconventional method using a brush may be used, and it is preferable toapply it on the opposed side faces as a whole. This is because thebonding part 12 plays a role of buffering (absorbing) thermal stress asstated above, in addition to the role of bonding the honeycomb segmentsmutually. Herein, the bonding material may be slurry, for example, whichis prepared by adding an additive such as organic binder, foamable resinor dispersing agent to a raw material including inorganic particles andcolloidal oxide, to which water is added, followed by kneading. Hereinexemplary inorganic particles include particles made of a ceramicmaterial containing one or two or more in combination of cordierite,alumina, aluminum titanate, silicon carbide, silicon nitride, mullite,zirconia, zirconium phosphate and titanic, or particles ofFe—Cr—Al-based metal, nickel-based metal and silicon (metalsilicon)-silicon carbide based composite materials. Exemplary colloidaloxide includes silica sol and alumina sol.

Next, the circumferential part of these plurality of honeycomb segments15 mutually bonded with the bonding material as a whole is cut so as toachieve a desired cross-sectional shape of the heat/acoustic waveconversion component 1 (e.g., a circle as in FIG. 12). Then, an outercoating material is applied to the circumferential face of the pluralityof honeycomb segments 15 after cutting as a whole, followed by drying,whereby a circumferential wall 13 is formed. Herein, the outer coatingmaterial used may be the same material as that of the bonding materialas stated above. A method for applying the outer coating material is notlimited especially, and for example, the coating material may be coatedwith a rubber spatula, for example, while rotating the honeycomb segmentbonded body on a wheel.

In this way, the bonded-type heat/acoustic wave conversion component 1in FIG. 12 is completed.

Next, the following describes a method for manufacturing thehigh-temperature side heat exchanger 2 in FIG. 3.

The heat-exchanging honeycomb structure 20 in the high-temperature sideheat exchanger 2 of FIG. 3 can be manufactured by a manufacturing methodsimilar to the method for manufacturing the monolithic heat/acousticwave conversion component 1 in FIG. 11 as stated above, other than thatmixture of carbon powder (e.g., graphite powder) with SiC powder is usedas the ceramic raw material and a die suitable for a honeycomb formedbody having a relatively large hydraulic diameter of cells is used asthe die for extrusion.

To manufacture this heat-exchanging honeycomb structure 20, for example,including a Si impregnated SiC composite material as a main component,it is preferable that a kneaded material prepared by mixing SiC powderwith carbon powder and kneading for adjustment is formed to be ahoneycomb formed body, then drying and sintering processing areperformed thereto, and then molten silicon (Si) is impregnated in thishoneycomb formed body. Such processing can form a configuration wherecoagulation of metal Si (metal silicon) surrounds the surface of SiCparticles after the sintering processing, and SiC particles are mutuallybonded via metal Si. Such a configuration can achieve high heatdurability and heat conductivity in spite of the dense configurationwith small porosity.

In addition to the molten silicon (Si), other metals such as Al, Ni, Cu,Ag, Be, Mg, and Ti may be used for impregnation. In this case, aftersintering, coagulation of metal Si (metal silicon) and other metals usedfor impregnation surrounds the surface of SiC particles, and SiCparticles are mutually bonded via metal Si and other metals used forimpregnation in the formed configuration. Such a configuration also canachieve high heat durability and heat conductivity in spite of the denseconfiguration with small porosity.

As the outer coating material of the heat-exchanging honeycomb structure20 as well, particles of silicon (metal silicon)-silicon carbide basedcomposite material is preferably used for the same reason as statedabove, among the particles made of the materials as stated above as thecandidates of inorganic particles of the material of the outer coatingmaterial (the material as the bonding material of the heat/acoustic waveconversion component 1).

It is preferable to perform slit formation processing to form a slit inthe cell penetrating direction at the circumferential wall formed by theapplication of the outer coating material. When the slit formationprocessing is performed, a heat resistant metal plate 21 d and a fin 21e may be formed when the high-temperature side annular tube 21 ismanufactured as described below.

The high-temperature side annular tube 21 on the high-temperature sideheat exchanger 2 in FIG. 3 is prepared by forming a material of highheat resistance to be an annular shape (herein, the annular shape suchthat a part of the wall face on the center side is partially omitted sothat, when being coupled with the heat-exchanging honeycomb structure20, a part of the circumferential wall of the heat-exchanging honeycombstructure 20 is exposed in the high-temperature side annular tube). Sucha material of high heat resistance is not limited especially, andspecific examples include metal such as stainless steel and copper ofhigh heat resistance and ceramic materials (e.g., those listed as thematerials of the heat/acoustic wave conversion component 1 in FIG. 11and the heat-exchanging honeycomb structure 20).

The high-temperature side heat exchanger 2 in FIG. 3 is completedbasically by assembling the heat-exchanging honeycomb structure 20 at acenter part that is a hole at the annular shape of the high-temperatureside annular tube 21.

Next the following describes a method for manufacturing thelow-temperature side heat exchanger 3 in FIG. 3. When a conventionallyknown heat exchanger is used as the low-temperature side heat exchanger3, a method for manufacturing such a conventionally known heat exchangercan be used. When the device having the same configuration as that ofthe high-temperature side heat exchanger 2 stated above is used as thelow-temperature side heat exchanger 3, the same manufacturing method asthat of the high-temperature side heat exchanger 2 as stated above canbe used.

As other members of the heat/acoustic wave conversion unit 100 in FIG.3, e.g., the metal member 32, the housing 100 a, and the interferencemember 1 a, those conventionally known can be used, and they can bemanufactured by a conventionally known method.

EXAMPLES

The following describes the present invention more specifically by wayof examples, and the present invention is by no means limited to theseexamples.

Example 1

In Example 1, cordierite forming raw material was used as the ceramicraw material. Then 35 parts by mass of dispersing medium, 6 parts bymass of organic binder, and 0.5 parts by mass of dispersing agent wereadded to 100 parts by mass of the cordierite forming raw material,followed by mixing and kneading to prepare a kneaded material. Thecordierite forming raw material used included 38.9 parts by mass of talcof 3 μm in average particle size, 40.7 parts by mass of kaolin of 1 μmin average particle size, 5.9 parts by mass of alumina of 0.3 μm inaverage particle size, and 11.5 parts by mass of boehmite of 0.5 μm inaverage particle size. Herein the average particle size refers to amedian diameter (d50) in the particle distribution of each raw material.

Water was used as the dispersing medium. Hydroxypropylmethylcellulosewas used as the organic binder. Ethylene glycol was used as thedispersing agent.

Next, the thus obtained kneaded material was extruded using a die, sothat a plurality of honeycomb formed bodies each including triangularcells and having a hexagonal overall shape were prepared. During thisextrusion, prior to the extrusion using a regular die corresponding tothe heat/acoustic wave conversion component of Example 1, the kneadedmaterial was extruded using a dummy die of about 0.07 mm in ribthickness. Then, using the kneaded material after the extrusion usingthis dummy die, extrusion using the real die was executed. At this time,the ratio of water in the kneaded material used for the extrusion usingthe real die was strictly controlled in the kneaded material componentso that it was 41 parts by mass (error was within ±1 part by mass) withreference to 100 parts by mass of the kneaded material solid component.

At this time, the retainer plate configuration in FIG. 20 was used asthe retainer plate configuration for the die. In this retainer plateconfiguration, the length L1 (see FIG. 20) of the slit was 0.5 mm, andthe length L2 (see FIG. 20) obtained by subtracting the height of thestep height from the slit length L1 was 0.2 mm. Then, the width W (seeFIG. 20) of the slit was 0.05 mm, and the distance d (see FIG. 20)between the retaining plate and the step height was 0.5 mm.

Then, this honeycomb formed body was dried by a microwave dryer, andthen was dried completely by a hot-air drier (first drying step), andthen both end faces of the honeycomb fainted body were cut so as toadjust the length of the honeycomb formed body in the cell penetratingdirection. Such a honeycomb formed body was dried by a hot-air drier,and then was fired at 1,445° C. for 5 hours (first firing step).

Next, slurry was prepared, including oxide particles of Mg, Si and Al,binder, surfactant, water and the like. Herein, the binder and thesurfactant were the same as those described above. Such slurry wasbrought into contact with the surface of the partition wall in each cellof the honeycomb formed body after the first firing step (inner wallface of each cell), whereby a surface layer was formed there, includingoxide particles of Mg, Si and Al to enter the pores on the surface ofthe partition wall (inner wall face of each cell) and reduce the poreson the surface (surface layer formation step). This surface layer wasformed by a flow-down method, in which droplets of slurry were droppeddown from the above into each cell of the honeycomb formed body afterthe first firing step to let the droplets flow down on the inner wallface of the cell. At this time, flowing-down of droplets of the slurrywas repeated a plurality of times, and after turning the honeycombformed body after the first firing step upside down, droplets of slurrywere allowed to flow down a plurality of times again.

Next, drying processing similar to the first drying step was performedto the honeycomb formed body after the surface layer formation step(second drying step). Then, firing processing similar to the firstfiring step was performed to the honeycomb formed body after the seconddrying step (second firing step).

Finally, the circumferential part of the honeycomb formed body after thesecond firing step was cut as needed to correct the shape to be around-pillar shape. Then, an outer coating material was applied to thecircumferential face of the honeycomb formed body after cutting,followed by drying, whereby a circumferential wall was formed. Herein,the outer coating material was slurry prepared by adding organic binder,foamable resin and dispersing agent to a raw material includingcordierite particles and silica sol, to which water was added andkneaded. As a method for applying the outer coating material, thecoating material was coated with a rubber spatula, for example, whilerotating the honeycomb formed body after cutting on a wheel.

Through these steps, the monolithic heat/acoustic wave conversioncomponent of Example 1 was finally completed.

As for the thus completed heat/acoustic wave conversion component ofExample 1, the following properties were measured, including: thehydraulic diameter HD of the cells in a plane perpendicular(perpendicular plane) to the cell penetrating direction; the three-pointbending strength of the heat/acoustic wave conversion component; thematerial strength of the material making up the heat/acoustic waveconversion component; the porosity in the perpendicular plane; thelength L between both end faces; the open frontal area at the end faces;the curvature radius at the corners of the cells in the perpendicularplane; the average thickness of the partition wall at a center regionsurrounded by a circle that was a concentric circle inside of a circularcross section of the heat/acoustic wave conversion component in theperpendicular plane and accounted for 80% of the area; and the averagethickness of the partition wall at the circumferential region that wasthe remaining region accounting for 20% of the circular cross section ofthe heat/acoustic wave conversion component in the perpendicular planeother than the center region.

The hydraulic diameter HD of the cells was obtained as follows. That is,an enlarged photo of the cross section of the heat/acoustic waveconversion component in the perpendicular plane was taken, and 10 cellsbelonging to the center region as stated above were selected at randomin this enlarged photo of the cross section. Then, the hydraulicdiameter of each was calculated by the expression to define thehydraulic diameter: HD=4×S/C, where S denotes the cross-sectional areaof the cell and C denotes the perimeter of this section, and thenaverage of them was calculated as the hydraulic diameter.

The three-point bending strength of the heat/acoustic wave conversioncomponent was obtained as follows. A rod-shaped member was cut out fromthe heat/acoustic wave conversion component to have a size that isspecified by JIS R1601 so as to have a length direction in the directionperpendicular to the penetrating direction of the cells. Then, thethree-point bending test jig was set so that the breaking position waslocated to the vicinity of the center which can be considered to belongto the center region of this rod-shaped member as stated above whilekeeping the distances between fulcrums that are specified by JIS R1601,and the three-point bending (bending) test was conducted in the lengthdirection. The maximum stress before the member breaks was measured.Similar measurement of the maximum stress was conducted to other ninesamples cut out from this heat/acoustic wave conversion component also.Then, the average of the measurements of the maximum stress was obtainedfor these ten samples obtained in total, and this average was set as thethree-point bending strength of the heat/acoustic wave conversioncomponent. Meanwhile, the material strength of the material making upthe heat/acoustic wave conversion component was measured as follows.Firstly, a member having the same shape as the rod member as statedabove was formed using a kneaded material as a raw material of thepartition wall, which was then dried and fired to prepare a sample.Next, the three-point bending (bending) test as stated above wasperformed to the sample, whereby the material strength was obtained. Theporosity was measured by mercury porosimeter (specifically product name:AutoPore IV9505 manufactured by Micromeritics Co.).

The open frontal area was obtained by taking an image of the crosssection in the perpendicular plane by a microscope, and finding thematerial-part area S1 and the gap-part area S2 from the image taken ofthe cross section. Then the open frontal area was obtained as S2/(S1+S2)based on S1 and S2. The curvature radius at the corners of the cells wasobtained by taking an enlarged photo of the cross section in theperpendicular plane and measuring the curvature of the corners based onthe cross-sectional shapes of the cells.

For the average thickness at the partition wall in the center region andthe average thickness of the partition wall at the circumferentialregion, ten groups each including mutually adjacent two cells wereselected at random from each of the regions, and the thickness at thepartition wall between the cells in each group was measured. Then theaverage was obtained for these ten groups.

Based on the measurement values obtained through the measurement asstated above, the following nine types of parameters were obtained. Thefollowing nine types of parameters include ones that are not independentmutually and change together with other parameters, but such parametersalso are described for the sake of descriptions.

(1) hydraulic diameter HD of the cells in a plane perpendicular(perpendicular plane) to the cell penetrating direction, (2) three-pointbending strength of the heat/acoustic wave conversion component, (3)material strength of the material making up the heat/acoustic waveconversion component, (4) porosity, (5) length L of the heat/acousticwave conversion component, (6) ratio of the hydraulic diameter HD to thelength L of the heat/acoustic wave conversion component, HD/L, (7) openfrontal area, (8) curvature radius at the corners of the cells, and (9)ratio of the thickness of the partition wall at a center region to thethickness of the partition wall at a circumferential region

The following Table 1 describes the values of these nine types ofparameters for the heat/acoustic wave conversion component of Example 1.Table 1 describes the segmented structure (bonded type or monolithictype) in addition to the value of parameters from (1) to (9).

TABLE 1 Partition wall thickness at 3-point bending circumference/ Cellstrength of Length L of Curvature partition hydraulic heat/acoustic waveMaterial heat/acoustic Hydraulic Open radius of wall thickness diameterconversion strength Poros- wave conversion diameter frontal cell cornersat center Bonding/ HD (mm) component (MPa) (MPa) ity (%) component (mm)HD/length L area (%) (mm) region monolithic Ex. 1 0.25 15 46 4 30 0.008374 0.05 1.3 Monolithic

The following experiments 1 and 2 were conducted using the heat/acousticwave conversion component of this Example 1.

Experiment 1 was as follows. Firstly, the heat/acoustic wave conversioncomponent of Example 1 was assembled in the power generation system 1000of FIG. 1, instead of the heat/acoustic wave conversion component 1.Then, exhaust gas from an automobile at about 500° C. was allowed toflow into the high-temperature side heat exchanger 2, and thetemperature of the exhaust gas flowing out whose temperature fell tosome extent was measured. Based on a temperature change at this time,the amount of heat flowing into this power generation system wascalculated. Due to the flowing-in of this exhaust gas, the end of theheat/acoustic wave conversion component on the side of thehigh-temperature side heat exchanger 2 had a temperature kept about at500° C. Meanwhile, water at 60° C. was allowed to flow into thelow-temperature side heat exchanger 3 so as to let the end of theheat/acoustic wave conversion component on the side of thelow-temperature side heat exchanger 3 keep the temperature at 60° C.Then, measurement was performed using a microphone or the like as theenergy converter of the power generation system 1000 of FIG. 1 as towhat degree of electric power was generated from acoustic waves by athermoacoustic effect due to the temperature difference between the bothends of the heat/acoustic wave conversion component as stated above.Then, a measurement value of the electric power amount was divided bythe energy conversion efficiency (efficiency to convert acoustic-waveenergy into electric power) of the microphone known beforehand, wherebyan estimated value of acoustic-wave energy was obtained. Then, based onthis estimated value of acoustic wave energy and the amount of heatflowing into the power generation system as stated above, energyconversion efficiency from heat to acoustic-wave energy was obtained.Evaluation was made using three grades, that is, when the energyconversion efficiency was 60% or more, the evaluation was “◯”. When theenergy conversion efficiency was 30% or more and less than 60%, theevaluation was “Δ”. When the energy conversion efficiency was less than30%, the evaluation was “X”. In this experiment, working fluid in thelooped tube 4, the resonant tube 5 and the cells causing self-inducedoscillations was helium gas at 10 atm.

Experiment 2 was as follows. Acoustic waves having the frequency and theamplitude at the same degree as the frequency and the amplitude ofacoustic waves generated by a thermoacoustic effect of heat/acousticwave conversion components were generated from a speaker, and suchacoustic waves were emitted continuously for 24 hours toward theheat/acoustic wave conversion component placed at a position close tothe speaker. Such an emission experiment was performed for the same tenpieces of the heat/acoustic wave conversion components, and theirbreakage probability was Weibull plotted, and then the breakageprobability under the designed stress was read therefrom.

Example 2 and Comparative Examples 1, 2

Heat/acoustic wave conversion components as Example 2 and ComparativeExamples 1 and 2 were manufactured by the same manufacturing method asthat of the manufacturing method of Example 1 as stated above exceptthat a die used for extrusion was different, where these heat/acousticwave conversion components were different from Example 1 only in thevalues of parameters (hydraulic diameter HD and HD/L) relating to thehydraulic diameter HD of the cells among the nine types of parameters asstated above.

Then, the two experiments 1 and 2 similar to those for Example 1 wereconducted for these Example 2 and Comparative Examples 1 and 2.

Examples 3 to 5 and Comparative Example 3

Heat/acoustic wave conversion components as Examples 3 to 5 weremanufactured by the same manufacturing method as that of themanufacturing method of Example 1 as stated above except that the amountof pore former in kneaded material was different, where theseheat/acoustic wave conversion components were different from Example 1only in the values of parameters (three-point bending strength, materialstrength and porosity) relating to the three-point bending strengthamong the nine types of parameters as stated above. Then a heat/acousticwave conversion components as Comparative Example 3 was manufactured bythe same manufacturing method as that of the manufacturing method ofExample 1 as stated above except that the amount of pore former inkneaded material was different and the surface-layer formation step wasnot conducted, where the heat/acoustic wave conversion component wasdifferent from Example 1 only in the values of parameters (three-pointbending strength, material strength and porosity) relating to thethree-point bending strength among the nine types of parameters asstated above.

Then, the two experiments 1 and 2 similar to those for Example 1 wereconducted for these Examples 3 to 5 and Comparative Example 3.

The following Table 2 shows the experimental results of Examples 1 to 5and Comparative Examples 1 to 3 as explained above, together with thevalues of parameters different from those of Example 1.

TABLE 2 Cell 3-point bending strength Damage hydraulic Hydraulic ofheat/acoustic wave Material Energy probability by diameter HD diameterconversion component strength conversion acoustic (mm) HD/length L (MPa)(MPa) Porosity (%) efficiency waves (%) Ex. 1 0.25 0.008 15 46 4 ∘ 0 Ex.2 0.4 0.013 15 46 4 ∘ 0 Comp. Ex. 1 0.5 0.017 15 46 4 x 0 Comp. Ex. 20.8 0.027 15 46 4 x 0 Ex. 3 0.25 0.008 12 30 6 ∘ 0.1 Ex. 4 0.25 0.008 1024 10 ∘ 2 Ex. 5 0.25 0.008 5 20 25 ∘ 3 Comp. Ex. 3 0.25 0.008 4.5 15 37∘ 100

In Table 2, as is found from a comparison between Examples 1, 2 andComparative Examples 1 and 2 having mutually different hydraulicdiameters HD of the cells (and ratios HD/L), Examples 1 and 2 had higherenergy conversion efficiency than Comparative Examples 1 and 2. Thisshows that the hydraulic diameter HD of cells of 0.4 mm or less isrequired to exert a large thermoacoustic effect.

In Table 2, as is found from a comparison between Examples 1, 3 to 5 andComparative Example 3 having mutually different three-point bendingstrengths (or material strength and porosity), Examples 1, 3 to 5 hadmuch less damage than Comparative Example 3. This shows that thethree-point bending strength of 5 MPa or more is required to avoiddamage. It is further found that the strength of the porous materialmaking up the heat/acoustic wave conversion component of 20 MPa or moreis required to avoid damage. Conversely based on the fact thatComparative Example 3 was extremely inferior in damage, it can be foundthat the surface layer formation step is preferable. Further, since nodamage was found only in Example 1 among Examples 1, 3 to 5, it can bethen found that the porosity of 5% or less is preferable.

Examples 6 to 10

Heat/acoustic wave conversion components as Examples 6 to 10 weremanufactured by the same manufacturing method as that of themanufacturing method of Example 1 as stated above except that the lengthof extrusion was different during extrusion, where these heat/acousticwave conversion components were different from Example 1 only in thevalues of parameters (length L of heat/acoustic wave conversioncomponent, and HD/L) relating to the length L of the heat/acoustic waveconversion component among the nine types of parameters as stated above.

Then, the two experiments 1 and 2 similar to those for Example 1 wereconducted for these Examples 6 to 10.

Examples 11 to 13

Heat/acoustic wave conversion components as Examples 11 to 13 weremanufactured by the same manufacturing method as that of themanufacturing method of Example 1 as stated above except that adifferent die was used for extrusion, where these heat/acoustic waveconversion components were different from Example 1 only in the valuesof open frontal area of the heat/acoustic wave conversion componentamong the nine types of parameters as stated above.

Then, the two experiments 1 and 2 similar to those for Example 1 wereconducted for these Examples 11 to 13.

The following Table 3 shows the experimental results of Examples 6 to 13as explained above, together with the values of parameters differentfrom those of Example 1.

TABLE 3 Length L of Damage heat/acoustic probability wave Hydraulic Openby conversion diameter frontal Energy acoustic component HD/length areaconversion waves (mm) L (%) efficiency (%) Ex. 6 3 0.083 74 Δ 0 Ex. 7 120.021 74 Δ 0 Ex. 8 15 0.017 74 ◯ 0 Ex. 9 50 0.005 74 ◯ 0 Ex. 10 60 0.00474 Δ 0 Ex. 11 30 0.083 80 ◯ 2 Ex. 12 30 0.083 93 ◯ 3 Ex. 13 30 0.083 95◯ 100

In Table 3, as is found from a comparison between Examples 6 to 10having mutually different ratios HD/L (and L), Examples 8 and 9 hadhigher energy conversion efficiency than Examples 6, 7 and 10. Thisshows that the ratio HD/L of 0.005 or more and less than 0.02 isrequired to exert a large thermoacoustic effect and to avoid damage.

In Table 3, as is found from a comparison between Examples 11 to 13having mutually different open frontal areas of the cells, Examples 11,12 had less damage than Example 13. This shows that the open frontalarea at the end faces of the heat/acoustic wave conversion component of93% or less is preferable to avoid damage.

Examples 14 to 19

Heat/acoustic wave conversion components as Examples 14 to 19 weremanufactured by the same manufacturing method as that of themanufacturing method of Example 1 as stated above except that adifferent die was used for extrusion, where these heat/acoustic waveconversion components were different from Example 1 only in the valuesof curvature radius at the cell corners among the nine types ofparameters as stated above.

Then, the two experiments 1 and 2 similar to those for Example 1 wereconducted for these Examples 14 to 19.

Examples 20 to 23

Heat/acoustic wave conversion components as Examples 20 to 23 weremanufactured by the same manufacturing method as that of themanufacturing method of Example 1 as stated above except that adifferent die was used for extrusion, where these heat/acoustic waveconversion components were different from Example 1 only in the valuesof the ratio of the partition wall thickness at a center region to thepartition wall thickness at a circumferential region among the ninetypes of parameters as stated above.

Then, the two experiments 1 and 2 similar to those for Example 1 wereconducted for these Examples 20 to 23.

Example 24

A heat/acoustic wave conversion component as Example 24 was manufacturedby the same manufacturing method as that of the manufacturing method ofExample 1 as stated above except that it included the step to bond aplurality of honeycomb segments, i.e., a plurality of honeycomb segmentswere prepared by the manufacturing method substantially similar to theforming of the honeycomb formed body of Example 1 and they were bondedwith a bonding material (the same as the outer coating material), wherethe heat/acoustic wave conversion component was different from Example 1only in that the segmented structure (bonded type/monolithic type) wasof a bonded type.

Then, the two experiments 1 and 2 similar to those for Example 1 wereconducted for this Example 24.

The following Table 4 shows the experimental results of Examples 14 to24 as explained above, together with the values of parameters differentfrom those of Example 1.

TABLE 4 Partition wall Damage Curvature thickness at Energy probabilityradius circumference/ conver- by of cell partition wall sion acousticcorners thickness at Bonding/ effi- waves (mm) center region monolithicciency (%) Ex. 14 0.005 1.3 Monolithic ◯ 2 Ex. 15 0.01 1.3 Monolithic ◯2 Ex. 16 0.02 1.3 Monolithic ◯ 0 Ex. 17 0.03 1.3 Monolithic ◯ 0 Ex. 180.08 1.3 Monolithic ◯ 0 Ex. 19 0.12 1.3 Monolithic Δ 0 Ex. 20 0.05 1.05Monolithic ◯ 0.1 Ex. 21 0.05 1.1 Monolithic ◯ 0 Ex. 22 0.05 2 Monolithic◯ 0 Ex. 23 0.05 2.05 Monolithic Δ 0 Ex. 24 0.05 1.3 Bonding ◯ 0

In Table 4, as is found from a comparison between Examples 14 to 19 thatwere different from Example 1 only in the value of curvature radius ofthe cell corners, Examples 16 to 18 had less damage than Examples 14 and15, and had higher energy conversion efficiency than Example 19. Thisshows that the curvature radius at the cell corners of 0.02 mm or moreand 0.1 mm or less is preferable for a larger thermoacoustic effect andto avoid damage.

In Table 4, as is found from a comparison between Examples 20 to 23 thatwere different from Example 1 only in the ratio of the partition wallthickness at a center region to the partition wall thickness at acircumferential region, Examples 21, 22 had less damage than Example 20,and had higher energy conversion efficiency than Example 23. This showsthat the ratio of the partition wall thickness at a center region to thepartition wall thickness at a circumferential region of 1.1 to 2.0 ispreferable for a larger thermoacoustic effect and to avoid damage.

In Table 4, as is found from a comparison between the bonded-typeExample 24 and the monolithic Example 1, Example 24 had the same degreeas that of Example 1 in the energy conversion efficiency as well asdamage by acoustic waves. This shows that the bonded-type also enablesthe functions to exert a large thermoacoustic effect and to avoiddamage.

Then, in order to confirm the effect of the two configurations duringextrusion as stated above, the following experiment for extrusion wasconducted for reference experiment.

(1) Extrusion for a heat/acoustic wave conversion component wasattempted by the same manufacturing method as that of Example 1 exceptthat the dummy die used had a rib thickness of 0.09 mm.

(2) Extrusion for a heat/acoustic wave conversion component wasattempted by the same manufacturing method as that of Example 1 exceptthat the dummy die used had a rib thickness of 0.10 mm.

(3) Extrusion for a heat/acoustic wave conversion component wasattempted by the same manufacturing method as that of Example 1 exceptthat the dummy die used had a rib thickness of 0.04 mm.

(4) Extrusion for a heat/acoustic wave conversion component wasattempted by the same manufacturing method as that of Example 1 exceptthat the dummy die used had a rib thickness of 0.03 mm.

(5) Extrusion for a heat/acoustic wave conversion component wasattempted by the same manufacturing method as that of Example 1 exceptthat the kneaded material used included water at the ratio in thekneaded material that was about 43 parts by mass (error was within ±1part by mass) with reference to 100 parts by mass of the kneadedmaterial solid component.

(6) Extrusion for a heat/acoustic wave conversion component wasattempted by the same manufacturing method as that of Example 1 exceptthat the kneaded material used included water at the ratio in thekneaded material that was about 39 parts by mass (error was within ±1part by mass) with reference to 100 parts by mass of the kneadedmaterial solid component.

As a result, forming was enabled without problems in (1) and (3), but in(2) and (6), clogging of the kneaded material occurred in the holes inthe forming die, and so forming failed. In (4), considerable pressurewas required for extrusion by the dummy die, which showed thepossibility of damage in the die, and so the experiment was stopped. In(5), the formed body obtained by the extrusion was deformed easily dueto the self weight, and a desired shape was not obtained.

Considering these results together with the successful result ofextrusion in Example 1, it can be found that pre-extrusion is preferablyperformed using a dummy die having a rib thickness of 0.04 mm or moreand 0.09 mm or less and the ratio of water in the kneaded material ispreferably 40 to 42 parts by mass with reference to 100 parts by mass ofthe kneaded material solid component.

The present invention is favorably used in a system that effectivelyuses heat from exhaust gas of automobiles or the like to generateelectric power and cold heat.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1: heat/acoustic wave conversion component    -   1 a: interference member    -   2, 2′, 2A, 2A′: high-temperature side heat exchanger    -   3: low-temperature side heat exchanger    -   4: looped tube    -   4′: looped tube    -   5: resonant tube    -   5′: transmission tube    -   6: energy converter    -   7: acoustic-wave generation part    -   11: partition wall    -   12: bonding part    -   12′: bonding part    -   13: circumferential wall    -   14: cell    -   15: honeycomb segment    -   15′: honeycomb segment    -   20: heat-exchanging honeycomb structure    -   20′: heat-exchanging honeycomb structure    -   20 a: partition wall    -   20 b: circumferential wall    -   20 c: slit    -   20 d: cell    -   20 s: contact face    -   21: high-temperature side annular tube    -   211: high-temperature side annular tube    -   212: high-temperature side annular tube    -   2110: in-tube honeycomb structure    -   2120: in-tube honeycomb structure    -   21 a: inflow port    -   21 b: outflow port    -   21 c: heat-receiving region    -   21 d: heat-resistance metal plate    -   21 e: fin    -   22, 23: honeycomb structure    -   23′: metal mesh member    -   22 a: metal outer tube    -   23 a: metal mesh outer tube    -   23 b: metalized layer    -   30: mesh lamination body    -   31: low-temperature side annular tube    -   31 a: inflow port    -   31 b: outflow port    -   32: metal member    -   301: die    -   303: second plate-shaped part    -   305: back hole    -   305 a, 309 a, 311 a; open end    -   306: second bonding face    -   307: first plate-shaped part    -   307 a: first layer    -   307 b: second layer    -   307 ba: other face of second layer    -   309: slit    -   310: first bonding face    -   311: hole part    -   313: cell block    -   401: die    -   402: retainer    -   403: rear retaining part    -   404: honeycomb formed body    -   405: gap    -   406: inclined face    -   407: opposed face    -   550: retainer plate configuration    -   552: slit    -   553: back hole    -   554: die    -   555: retaining plate    -   557: gap part    -   558: retaining jig    -   55 a: rear-retaining plate    -   561: extruded forming raw material    -   571: inside part    -   572: circumference part    -   573, 574: slit    -   575: step height    -   602, 702: slit    -   603, 703: back hole    -   604, 704: die    -   605, 705: retaining plate    -   615, 715: step height    -   100: heat/acoustic wave conversion unit    -   200: heat/acoustic wave conversion unit    -   100 a: housing    -   1000: power generation system    -   2000: cold heat generation system

What is claimed is:
 1. A heat/acoustic wave conversion component havinga first end face and a second end face, comprising a partition wall thatdefines a plurality of cells extending from the first end face to thesecond end face, inside of the cells being filled with working fluidthat oscillates to transmit acoustic waves, the heat/acoustic waveconversion component mutually converting heat exchanged between thepartition wall and the working fluid and energy of acoustic wavesresulting from oscillations of the working fluid, wherein hydraulicdiameter HD of the heat/acoustic wave conversion component is 0.4 mm orless, where the hydraulic diameter HD is defined as HD=4×S/C, where Sdenotes an area of a cross section of each cell perpendicular to thecell extending direction and C denotes a perimeter of the cross section,and the heat/acoustic wave conversion component has three-point bendingstrength of 5 MPa or more.
 2. The heat/acoustic wave conversioncomponent according to claim 1, wherein let that the heat/acoustic waveconversion component has a length L from the first end face to thesecond end face, a ratio HD/L of the hydraulic diameter HD to the lengthL of the heat/acoustic wave conversion component is 0.005 or more andless than 0.02.
 3. The heat/acoustic wave conversion component accordingto claim 2, wherein the heat/acoustic wave conversion component has anopen frontal area at each end face of 93% or less.
 4. The heat/acousticwave conversion component according to claim 3, wherein the cells have across-sectional shape that is perpendicular to the extending directionthat is a polygonal shape with curved corners, the corners of the shapehaving a curvature radius of 0.02 mm or more and 0.1 mm or less.
 5. Theheat/acoustic wave conversion component according to claim 4, whereinthe heat/acoustic wave conversion component comprises a porous materialhaving porosity of 5% or less.
 6. The heat/acoustic wave conversioncomponent according to claim 5, wherein in a plane perpendicular to theextending direction, the heat/acoustic wave conversion component has afirst average thickness of the partition wall at a center regionincluding a centroid of a cross-section of the heat/acoustic waveconversion component and having a shape similar to the cross section,and a second average thickness of the partition wall at acircumferential region that is located outside of the center region andaccounts for 20% of an area of the cross-section of the heat/acousticwave conversion component, the second average thickness being 1.1 to 2.0times the first average thickness.
 7. The heat/acoustic wave conversioncomponent according to claim 6, wherein the heat/acoustic waveconversion component includes: a plurality of honeycomb segments, eachincluding a partition wall that defines some of the plurality of cellsand mutually converting heat exchanged between the partition wall andthe working fluid and energy of acoustic waves resulting fromoscillations of the working fluid; a bonding part that mutually bondsside faces of the plurality of honeycomb segments; and a circumferentialwall that surrounds a circumferential face of a honeycomb structure bodymade up of the plurality of honeycomb segments and the bonding part. 8.The heat/acoustic wave conversion component according to claim 4,wherein the heat/acoustic wave conversion component comprises a porousmaterial having material strength of 20 MPa or more.
 9. Theheat/acoustic wave conversion component according to claim 8, wherein ina plane perpendicular to the extending direction, the heat/acoustic waveconversion component has a first average thickness of the partition wallat a center region including a centroid of a cross-section of theheat/acoustic wave conversion component and having a shape similar tothe cross section, and a second average thickness of the partition wallat a circumferential region that is located outside of the center regionand accounts for 20% of an area of the cross-section of theheat/acoustic wave conversion component, the second average thicknessbeing 1.1 to 2.0 times the first average thickness.
 10. Theheat/acoustic wave conversion component according to claim 9, whereinthe heat/acoustic wave conversion component includes: a plurality ofhoneycomb segments, each including a partition wall that defines some ofthe plurality of cells and mutually converting heat exchanged betweenthe partition wall and the working fluid and energy of acoustic wavesresulting from oscillations of the working fluid; a bonding part thatmutually bonds side faces of the plurality of honeycomb segments; and acircumferential wall that surrounds a circumferential face of ahoneycomb structure body made up of the plurality of honeycomb segmentsand the bonding part.
 11. The heat/acoustic wave conversion componentaccording to claim 1, wherein the heat/acoustic wave conversioncomponent has an open frontal area at each end face of 93% or less. 12.The heat/acoustic wave conversion component according to claim 1,wherein the cells have a polygonal shape with curved corners as across-sectional shape that is perpendicular to the extending direction,and the corners of the shape have a curvature radius of 0.02 mm or moreand 0.1 mm or less.
 13. The heat/acoustic wave conversion componentaccording to claim 1, wherein the heat/acoustic wave conversioncomponent includes a porous material having porosity of 5% or less. 14.The heat/acoustic wave conversion component according to claim 1,wherein the heat/acoustic wave conversion component comprises a porousmaterial having material strength of 20 MPa or more.
 15. Theheat/acoustic wave conversion component according to claim 1, wherein ina plane perpendicular to the extending direction, the heat/acoustic waveconversion component has a first average thickness of the partition wallat a center region including a centroid of a cross-section of theheat/acoustic wave conversion component and having a shape similar tothe cross section, and a second average thickness of the partition wallat a circumferential region that is located outside of the center regionand accounts for 20% of an area of the cross-section of theheat/acoustic wave conversion component, the second average thicknessbeing 1.1 to 2.0 times the first average thickness.
 16. Theheat/acoustic wave conversion component according to claim 1, whereinthe heat/acoustic wave conversion component includes: a plurality ofhoneycomb segments, each including a partition wall that defines some ofthe plurality of cells and mutually converting heat exchanged betweenthe partition wall and the working fluid and energy of acoustic wavesresulting from oscillations of the working fluid; a bonding part thatmutually bonds side faces of the plurality of honeycomb segments; and acircumferential wall that surrounds a circumferential face of ahoneycomb structure body made up of the plurality of honeycomb segmentsand the bonding part.
 17. A method for manufacturing the heat/acousticwave conversion component according to claim 1, comprising: a formingstep of extruding a forming raw material containing a raw material ofthe porous material to prepare a honeycomb formed body including apartition wall that defines a plurality of cells extending from a firstend face to a second end face, a first drying/firing step ofdrying/firing the honeycomb formed body prepared by the forming step; asurface layer formation step of bringing a surface of the partition wallin the cell of the honeycomb formed body fired at the firstdrying/firing step into a liquid body including at least one type ofmetal oxide particles of Mg, Si and Al so as to form a surface layerincluding the at least one type of metal oxide particles and enteringpores on the surface to reduce the pores on the surface; and a seconddrying/firing step of drying/firing the honeycomb formed body havingreduced pores on the surface by the surface layer formation step.
 18. Aheat/acoustic wave conversion unit, comprising the heat/acoustic waveconversion component according to claim 1, in a state where inside ofthe plurality of cells is filled with the working fluid, when there is atemperature difference between a first end part on the first end faceside and a second end part on the second end face side, theheat/acoustic wave conversion component oscillating the working fluidalong the extending direction in accordance with the temperaturedifference and generating acoustic waves; and a pair of heat exchangersthat are disposed in a vicinity of the first end part and the second endpart of the heat/acoustic wave conversion component, respectively, theheat exchangers exchanging heat with the both end parts to give atemperature difference between the both end parts.
 19. A heat/acousticwave conversion unit comprising: the heat/acoustic wave conversioncomponent according to claim 1, in a state where inside of the pluralityof cells is filled with the working fluid, and when the working fluidoscillates along the extending direction while receiving acoustic wavestransmitted, the heat/acoustic wave conversion component generating atemperature difference between a first end part on the first end faceside and a second end part on the second end face side in accordancewith oscillations of the working fluid; a heat exchanger that isdisposed in a vicinity of one of the first end part and the second endpart of the heat/acoustic wave conversion component, the heat exchangersupplying heat to the one end part or absorbing heat from the one endpart to keep a temperature at the one end part constant; and a hotheat/cold heat output unit that is disposed in a vicinity of the otherend part of the first end part and the second end part of theheat/acoustic wave conversion component that is on the opposite side ofthe one end part, the hot heat/cold heat output unit outputting hot heator cold heat obtained from exchanging of heat with the other end part sothat, in a state where the temperature of the one end part is keptconstant by the heat exchanger and when the heat/acoustic waveconversion component receives acoustic waves transmitted, the other endpart has a temperature difference in accordance with oscillations of theworking fluid due to transmission of the acoustic waves with referenceto the one end part kept at the constant temperature.